Brian Madden posted an excellent and to-the-point article on how TS CAL’s work. The emphasis was on those clients that do not have local storage.
As he points out in a respnse to reader feedback, User based TS CAL’s are different. Up to now, Windows 2003 has not tracked their usage. A Terminal Server simply checks to see if a license server is valid, if the license types match (user VS device) and if that there are user CAL’s available. No CAL’s are counted or issued. This is very likely to change with Windows "Longhorn". Like I said, this is just with User CAL’s. Read Brian’s article to see how TS CAL’s work.