I just upgraded to Firefox 2.0 yesterday (several months late) and I immediately noticed a problem:  Accesskeys and keyboard shortcuts don't work.  Sites like Gmail and Bloglines use keyboard shortcuts extensively, and even my site uses a few accesskeys to make life easier.  I searched and found an article that mentioned the problem, and it offered a simple solution:  Go to about:config, go to "ui.key.contentAccess" and change the value to "4".  Problem solved. 

Other than that, I have three thoughts about this new version: 

1. The spell check feature is amazing.
2. Websites look more like Internet Explorer's version now (I don't know if this is good or bad).
3. The close button on each tab is an obvious feature that should've been there in the first place, so now I don't have to use the TabFX extension.