Web application state and Undo issues

http://blogs.zdnet.com/Stewart/?p=515&tag=nl.e539
http://www.vanderwal.net/random/entrysel.php?blog=1665
http://weblogs.macromedia.com/jd/archives/2005/05/representing_ap.cfm
http://www.boagworld.com/archives/2007/06/the_importance_of_undo.html