One more note. As of last month (May) Thunderbird 2.0 had some bugs. Check out this Thunderbird Forum thread, especially the May 18th post:
http://forums.mozillazine.org/viewtopic.php?t=550079
Thanks. I’ve been on 2.0 pretty much since it was released. Seems to work o.k. for me. Then again, I have 95% of my spam filtering happening at my email provider.