I just upgraded to Wordpress 2.1. That was a huge pain in the ass. First, I decided it would be a good idea to start using the debian package to handle my wordpress updates. Not a good idea. There were bugs all over the place that I just now got fixed. But, there was still another problem: All of my custom pages were turned into categories and I had to manually go through and convert them back.
On the plus side, I like how everything feels a lot snappier. I read through their changelog and it looks as though they had a SQL expert from MySQL look over and optimize all of their queries. Kudos.