True, but you can stop something else working.
What i have found in the past is that companies use stange keys in hidden places where you will not normally expect them in order to handle time limits.
The best way round this is to use a registry TRACKER program which shows changes to the registry before and after a certain program has been installed.
This allows you to show what key the program has created or changed upon installation. The best bet is to run the tracker to get a registry snapshot - then install the program AND run it for the first time so that the date key is set - then run the tracker software agian and do another snapshot - this can then show you the differences and the keys that were created.
There a quite a few programs which do this if you have a look around - one of them is Regspy which you can find here -
http://www.utils32.com/regspy.asp
Good luck