Opens the UserEnv log that is stored under %SYSTEMROOT%\Debug\UserMode. This file contains a lot of useful information concerning the application of group policies. Sample UserEnv.log entries are:
 

USERENV(e8.408) 17:21:30:895 ProcessGPOs:
USERENV(e8.408) 17:21:30:965 ProcessGPOs:
USERENV(e8.408) 17:21:30:965 ProcessGPOs:  Starting computer Group Policy processing...
USERENV(e8.408) 17:21:30:965 ProcessGPOs:
USERENV(e8.408) 17:21:30:965 ProcessGPOs:
USERENV(e8.408) 17:21:30:965 ProcessGPOs:  Verbose output to eventlog requested.
USERENV(e8.408) 17:21:30:965 EnterCriticalPolicySection: Machine critical section has been claimed.  Handle = 0x5a4
USERENV(e8.408) 17:21:30:975 ProcessGPOs:  Machine role is 2.
USERENV(e8.408) 17:21:30:975 PingComputer:  First time:  0
USERENV(e8.408) 17:21:30:975 PingComputer:  Fast link.  Exiting.
USERENV(e8.408) 17:21:30:975 ProcessGPOs:  User name is:  CN=REGALTANG2,CN=Computers,DC=reeftank,DC=com, Domain name is:  REEFTANK
USERENV(e8.408) 17:21:30:975 ProcessGPOs: Domain controller is:  \\student2.reeftank.com  Domain DN is reeftank.com
USERENV(e8.408) 17:21:30:975 ReadGPExtensions: Failed to query for the function name.
USERENV(e8.408) 17:21:30:975 ProcessGPOs: Calling GetGPOInfo for normal policy mode
USERENV(e8.408) 17:21:30:975 GetGPOInfo:  ********************************
USERENV(e8.408) 17:21:30:975 GetGPOInfo:  Entering...
USERENV(e8.408) 17:21:30:985 GetGPOInfo:  Server connection established.
USERENV(e8.408) 17:21:30:995 GetGPOInfo:  Bound successfully.
USERENV(e8.408) 17:21:31:005 SearchDSObject:  Searching 
USERENV(e8.408) 17:21:31:015 SearchDSObject:  Found GPO(s):  <[LDAP://CN={84757F3E-0F51-4B20-A6BF-A7ACB89098F0},CN=Policies,CN=System,DC=reeftank,DC=com;0][LDAP://CN={1310A75E-337C-4074-86C7-B492370B0659},CN=Policies,CN=System,DC=reeftank,DC=com;0][LDAP://CN={31B2F340-016D-11D2-945F-00C04FB984F9},CN=Policies,CN=System,DC=reeftank,DC=com;2]>
USERENV(e8.408) 17:21:31:015 ProcessGPO:  ==============================
USERENV(e8.408) 17:21:31:015 ProcessGPO:  Deferring search for 
USERENV(e8.408) 17:21:31:025 ProcessGPO:  ==============================
USERENV(e8.408) 17:21:31:025 ProcessGPO:  Deferring search for 
USERENV(e8.408) 17:21:31:025 ProcessGPO:  ==============================
USERENV(e8.408) 17:21:31:025 ProcessGPO:  Deferring search for 
USERENV(e8.408) 17:21:31:025 GetGPOInfo:  No site name defined.  Skipping site policy.
USERENV(e8.408) 17:21:31:025 ProcessGPO:  ==============================
USERENV(e8.408) 17:21:31:035 ProcessGPO:  Searching 
USERENV(e8.408) 17:21:31:035 ProcessGPO:  Machine has access to this GPO.
USERENV(e8.408) 17:21:31:035 ProcessGPO:  Found functionality version of:  2
USERENV(e8.408) 17:21:31:035 ProcessGPO:  Found file system path of:  <\\reeftank.com\sysvol\reeftank.com\Policies\{31B2F340-016D-11D2-945F-00C04FB984F9}>
USERENV(e8.408) 17:21:31:075 ProcessGPO:  Found common name of:  <{31B2F340-016D-11D2-945F-00C04FB984F9}>
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Found display name of:  
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Found machine version of:  GPC is 5, GPT is 5
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Found flags of:  0
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Found extensions:  [{35378EAC-683F-11D2-A89A-00C04FBBCFA2}{53D6AB1B-2488-11D1-A28C-00C04FB94F17}][{827D319E-6EAC-11D2-A4EA-00C04F79F83A}{803E14A0-B4FB-11D0-A0D0-00A0C90F574B}][{B1BE8D72-6EAC-11D2-A4EA-00C04F79F83A}{53D6AB1B-2488-11D1-A28C-00C04FB94F17}]
USERENV(e8.408) 17:21:31:085 ProcessGPO:  ==============================
USERENV(e8.408) 17:21:31:085 ProcessGPO:  ==============================
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Searching 
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Machine has access to this GPO.
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Found functionality version of:  2
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Found file system path of:  <\\reeftank.com\SysVol\reeftank.com\Policies\{84757F3E-0F51-4B20-A6BF-A7ACB89098F0}>
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Found common name of:  <{84757F3E-0F51-4B20-A6BF-A7ACB89098F0}>
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Found display name of:  
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Found machine version of:  GPC is 0, GPT is 0
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Found flags of:  0
USERENV(e8.408) 17:21:31:085 ProcessGPO:  No client-side extensions for this object.
USERENV(e8.408) 17:21:31:085 ProcessGPO:  GPO This is a test of a reallyreallyreallyreallyreallyreallyreallyreallyreallyreallyreallyreally long policy name doesn't contain any data since the version number is 0.  It will be skipped.
USERENV(e8.408) 17:21:31:085 ProcessGPO:  ==============================
USERENV(e8.408) 17:21:31:085 ProcessGPO:  ==============================
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Searching 
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Machine has access to this GPO.
USERENV(e8.408) 17:21:31:085 ProcessGPO:  Found functionality version of:  2
USERENV(e8.408) 17:21:31:095 ProcessGPO:  Found file system path of:  <\\reeftank.com\SysVol\reeftank.com\Policies\{1310A75E-337C-4074-86C7-B492370B0659}>
USERENV(e8.408) 17:21:31:095 ProcessGPO:  Found common name of:  <{1310A75E-337C-4074-86C7-B492370B0659}>
USERENV(e8.408) 17:21:31:095 ProcessGPO:  Found display name of:  
USERENV(e8.408) 17:21:31:095 ProcessGPO:  Found machine version of:  GPC is 1, GPT is 1
USERENV(e8.408) 17:21:31:095 ProcessGPO:  Found flags of:  0
USERENV(e8.408) 17:21:31:095 ProcessGPO:  Found extensions:  [{35378EAC-683F-11D2-A89A-00C04FBBCFA2}{0F6B957D-509E-11D1-A7CC-0000F87571E3}]
USERENV(e8.408) 17:21:31:095 ProcessGPO:  ==============================
USERENV(e8.408) 17:21:31:115 GetGPOInfo:  Leaving with 1
USERENV(e8.408) 17:21:31:125 GetGPOInfo:  ********************************
USERENV(e8.408) 17:21:31:125 DebugPrintGPOList: List of GPO(s) to process: "Local Group Policy" "Domain Policy 2" "Default Domain Policy" 
USERENV(e8.408) 17:21:31:135 ProcessGPOs: OpenThreadToken failed with error 1008, assuming thread is not impersonating
USERENV(e8.408) 17:21:31:135 ProcessGPOs: -----------------------
USERENV(e8.408) 17:21:31:135 ProcessGPOs: Processing extension Registry
USERENV(e8.408) 17:21:31:135 DebugPrintGPOList: List of GPO(s) to process: "Local Group Policy" "Domain Policy 2" "Default Domain Policy" 
USERENV(e8.408) 17:21:31:135 CompareGPOLists:  The lists are the same.
USERENV(e8.408) 17:21:31:135 CheckGPOs: No GPO changes and no security group membership change and extension Registry has NoGPOChanges set.
USERENV(e8.408) 17:21:31:135 ProcessGPOs: -----------------------
USERENV(e8.408) 17:21:31:135 ProcessGPOs: -----------------------
USERENV(e8.408) 17:21:31:135 ProcessGPOs: Processing extension Folder Redirection
USERENV(e8.408) 17:21:31:135 ProcessGPOs: Extension Folder Redirection skipped with flags 0x90007.
USERENV(e8.408) 17:21:31:135 ProcessGPOs: -----------------------
USERENV(e8.408) 17:21:31:135 ProcessGPOs: Processing extension Microsoft Disk Quota
USERENV(e8.408) 17:21:31:135 ProcessGPOs: Extension Microsoft Disk Quota skipped with flags 0x90007.
USERENV(e8.408) 17:21:31:135 ProcessGPOs: -----------------------
USERENV(e8.408) 17:21:31:135 ProcessGPOs: Processing extension Scripts
USERENV(e8.408) 17:21:31:135 DebugPrintGPOList: List of GPO(s) to process: 
USERENV(e8.408) 17:21:31:135 CompareGPOLists:  The lists are the same.
USERENV(e8.408) 17:21:31:135 CheckGPOs: No GPO changes but couldn't read extension Scripts's status or policy time.
USERENV(e8.408) 17:21:31:135 ProcessGPOs: Extension Scripts skipped because both deleted and changed GPO lists are empty.
USERENV(e8.408) 17:21:31:135 ProcessGPOs: -----------------------
USERENV(e8.408) 17:21:31:135 ProcessGPOs: Processing extension Security
USERENV(e8.408) 17:21:31:145 DebugPrintGPOList: List of GPO(s) to process: "Default Domain Policy" 
USERENV(e8.408) 17:21:31:145 CompareGPOLists:  The lists are the same.
USERENV(e8.408) 17:21:31:145 CheckGPOs: No GPO changes but extension Security's MaxNoGPOListChangesInterval has been exceeded.
USERENV(e8.408) 17:21:31:145 ProcessGPOList: Entering for extension Security
USERENV(e8.408) 17:21:35:491 ProcessGPOList: Extension Security returned 0x0.
USERENV(e8.408) 17:21:35:501 ProcessGPOs: -----------------------
USERENV(e8.408) 17:21:35:511 ProcessGPOs: -----------------------
USERENV(e8.408) 17:21:35:511 ProcessGPOs: Processing extension Internet Explorer Branding
USERENV(e8.408) 17:21:35:511 DebugPrintGPOList: List of GPO(s) to process: 
USERENV(e8.408) 17:21:35:511 CompareGPOLists:  The lists are the same.
USERENV(e8.408) 17:21:35:511 CheckGPOs: No GPO changes but couldn't read extension Internet Explorer Branding's status or policy time.
USERENV(e8.408) 17:21:35:511 ProcessGPOs: Extension Internet Explorer Branding skipped because both deleted and changed GPO lists are empty.
USERENV(e8.408) 17:21:35:511 ProcessGPOs: -----------------------
USERENV(e8.408) 17:21:35:511 ProcessGPOs: Processing extension EFS recovery
USERENV(e8.408) 17:21:35:511 DebugPrintGPOList: List of GPO(s) to process: "Local Group Policy" "Default Domain Policy" 
USERENV(e8.408) 17:21:35:511 CompareGPOLists:  The lists are the same.
USERENV(e8.408) 17:21:35:511 CheckGPOs: No GPO changes and no security group membership change and extension EFS recovery has NoGPOChanges set.
USERENV(e8.408) 17:21:35:511 ProcessGPOs: -----------------------
USERENV(e8.408) 17:21:35:511 ProcessGPOs: -----------------------
USERENV(e8.408) 17:21:35:511 ProcessGPOs: Processing extension Application Management
USERENV(e8.408) 17:21:35:511 ProcessGPOs: Extension Application Management skipped with flags 0x90007.
USERENV(e8.408) 17:21:35:511 ProcessGPOs: -----------------------
USERENV(e8.408) 17:21:35:511 ProcessGPOs: Processing extension IP Security
USERENV(e8.408) 17:21:35:511 DebugPrintGPOList: List of GPO(s) to process: 
USERENV(e8.408) 17:21:35:511 CompareGPOLists:  The lists are the same.
USERENV(e8.408) 17:21:35:511 CheckGPOs: No GPO changes but couldn't read extension IP Security's status or policy time.
USERENV(e8.408) 17:21:35:521 ProcessGPOs: Extension IP Security skipped because both deleted and changed GPO lists are empty.
USERENV(e8.408) 17:21:35:521 LeaveCriticalPolicySection: Critical section 0x5a4 has been released.
USERENV(e8.408) 17:21:35:521 ProcessGPOs: Computer Group Policy has been applied.
USERENV(e8.408) 17:21:35:521 ProcessGPOs: Leaving with 1.
USERENV(e8.408) 17:21:35:521 GPOThread:  Next refresh will happen in 5 minutes
USERENV(e8.6e4) 17:21:35:531 PolicyChangedThread: Entering with 1.
USERENV(e8.6e4) 17:21:35:661 PolicyChangedThread: Leaving
USERENV(5d4.288) 17:21:50:292 LibMain: Process Name:  C:\Documents and Settings\Administrator\Start Menu\Programs\Startup\mp3.exe
USERENV(5d4.288) 17:21:50:442 LibMain: Process Name:  C:\Documents and Settings\Administrator\Start Menu\Programs\Startup\mp3.exe
USERENV(5d4.288) 17:21:50:472 LibMain: Process Name:  C:\Documents and Settings\Administrator\Start Menu\Programs\Startup\mp3.exe
USERENV(5d4.288) 17:25:30:384 LibMain: Process Name:  C:\Documents and Settings\Administrator\Start Menu\Programs\Startup\mp3.exe
USERENV(5d4.288) 17:25:30:494 LibMain: Process Name:  C:\Documents and Settings\Administrator\Start Menu\Programs\Startup\mp3.exe
USERENV(5d4.288) 17:25:30:514 LibMain: Process Name:  C:\Documents and Settings\Administrator\Start Menu\Programs\Startup\mp3.exe