Some users of your script have noticed strange character encoding problems. For example, the ¬ character doesn't work right. Here are a few screenshots...
http://img265.imageshack.us/img265/1086/sswsnx4.png
http://img252.imageshack.us/img252/49/83648818pt9.png (before refresh)
http://img444.imageshack.us/img444/6457/71502228do6.png (after)
I think the XMLHttpRequest is to blame. Do you have any ideas for how to fix this?
Update: I added charset=iso-8859-1 to the HTTP headers, and that seems to help, at least with viewing messages. There may still be issues with sending messages, but I haven't tested that.