I can’t get into the exact details here, but suffice it to say, that when you stray out of the standard viewstate-sandbox (ie LoadPagestateFromPersistenceMediume & SavePageStateToPersistenceMedium), be very careful.  Once you get viewstate out of that page and you consider users who use multiple browser tabs (yet with the same application session, or worse, new windows launched with Ctrl+N) there are a few subtle design considerations.  This guy’s article provides one solution.   If you also deal with multiple nodes (like a Web Farm), just persist to a shared location (Network share, NAS, whatever).

J