I downloaded and installed the firefox 4 beta/release candidate today and I seem to like it, the only thing I have to say is that I think they tried to copy chrome too much, now it looks more like chrome than anything else, but I found a few pros and cons of the new version

Pro's
+Faster
+Better Win7 features
+Lighter

Con's
-New format, kinda hard to find things.
-Plug ins not compatible
-Typing into the address bar doesn't use Google 'I'm feeling lucky'

But other than that its allright! Reccommended still!