I have upgraded to wordpress 2.1 and so far so good. I am sorry the site was a bit screwy earlier today, but who knew that upgrading from wordpress 1.5.1.3 straight to 2.1 would cause your theme and umm everything else to break. Oh well, everything seems to work now and lucky for me the database tables all seem to have survived.
My fist impressions with 2.1 are that its very slick on the back end, I really am digging the widgets feature, I am going to writing a few of them, I had custom hacked my old upload file feature so this new one is going to need a little hacking as well. Frankly its horrible that the thumbnail feature is so bad after so long. But you know a little hacking keeps you strong.
If you notice anything that seems to be broken let me know.