The "crippleware" approach consists on disabling some features of your program until user's registration. (Example: you could disable the open, save or print options; use nag screens or create any other limitation.)

ActiveLock can help you to lock any features of your program by detecting user registration.

NOTE: There is a serious drawback with this approach: if your users can't evaluate your program, they're not going to register it. Therefore, avoid disabling features that are really important to the operation of your software.

See also: RegisteredUser property.