I finally made the switch last night. The only problem that I encountered is that Thunderbird didn't import my Mozilla email correctly, probably due to the fact that I haven't done a clean install in years, so there are settings in my prefs files from a very long time ago. I was able to work around that, and everything seems to be working well now.
I keep my broswer/email synchronized between my laptop and desktop. The browser portion of it is easier because of the bookmark extensions for Firefox - which is really the only thing I need to synch. I still have to manually copy files for email, but at least the number of files I have to copy is smaller now.
Anyway, both are nice improvements, and I'm glad I finally made the switch. The only thing I miss is the ease with which you can launch mail from Mozilla, and vice-versa.