I like the new look of Firefox 2.0 but I can't say I've noticed any other noticeable improvements.
I have noticed new problems, however.
The one that is annoying me most is that, sometimes when I open a new tab the keyboard focus does not move to the address bar. Sounds trivial but is actually infuriating.
I still use Firefox as my default browser but IE7.0 is certainly going to give them a run for their money.