On http://www.RunSaturday.com I was using DNN's roles for friends... then one day I couldn't log on.
The reason? I had too many friends :)
Basically the problem was that DNN was inserting a very long string into a cookie....
To work around this I'll need to either change my code to not use the DNN roles structure or insert an HTTPModule to tweak their Roles behaviour.
Here's the DNN thread: http://www.dotnetnuke.com/Community/Forums/tabid/795/forumid/111/threadid/234880/scope/posts/threadpage/7/Default.aspx