Registration is different than activation. Registration is a way to stay in touch for both the company (Adobe) and the user (you). It also helps in support issues that may arise. Periodically I receive request to update my registration which serves as a reminder to check my registration to ensure it is still accurate information.
There are no rules for good photographs, there are only good photographs
I have read a little about Adobe's annual licensing of Photoshop (I believe for CS 5 and above). I have CS3 and CS4 and keep getting messages from Adobe to register. I registered both long, long ago. Can a company change the licensing agreement on older, superseded software?
Please check out our sister group, attachments allowed-Photoshop by Example http://groups.yahoo.com/group/ps-by-ex/