I've been running FF3 since beta 1 on 2 machines and I've been quite satisfied with it. I
would go as far as to say that it's been more stable than FF2. I have experienced my profile
"go bad" which meant that it wouldn't start. That's quite some time ago though, I think it was
while beta 2 was the latest.
I like the awesome bar. Once you get used to how it works it is a very nice improvement.
What I like the most though is all the work they have done on fixing the memory leaks and
performance. It was very much needed and they have certainly delivered.