Im storing session-like data pickled inside the URL. I end up with long, ugly-looking URLs, but it does mean that a browser's bookmarks and back button work as expected, effectively 'undoing' changes made to thier session state.

This solution also avoids the problem of finding enough storage on the server to store multiple revisions of each session.

This solution is common and works great, but Ive never really liked it myself since it involves munging URL's and making them look ugly. I like nice short URL's I can email. In my more situation specific solution I give access to the stored session snapshots along the lines of ....?load_ssn=Default will load in the session named "Default" for that user allowing them to be bookmarked... -- Andy McKay.