Just commenting:

1.Security is relative. There is no 100% secure way to protect from anything.

2. There always are(will be) "free-riders". (in the world of IT they are known as crackers and warez-users (the first group "makes" warez for the second from commercial apps))

3. If you are thinking about some kind of Registry protection beware of tools (should make check for their existance, but it can be always fooled) like: uninstallers (for example CleanSweep can be used for logging changes made to registry), Registry loggers, Loader applications (something that is started prior your app in order to fool your registry check and/or time check, etc.

4. The bigger part of your users is supposed to not know how to "crack" your app.

Kind Regards