I wasn't impressed with Thunderbird either. I'm sticking with Outlook/SpamBayes. I am a Firefox convert, though. I switched about a week ago and I'm hooked on the tabbed browsing and all the extensions.

I do miss PopupCop a bit. It's a better blocker then what is built-in Firefox (or the IE Google toolbar) and it's got some other features I like. Hmmmm.... maybe I'll learn how to write a Firefox extension.