We've been running tests and found that IE7 renders pages a lot faster than FF2, but the security of IE7 is a lot tighter than it ever has been before, and sometimes annoyingly so!
IE7 seems to do everything that FF2 does, and FF2 doesn't really have that many new features over 1.5 tbh, but I guess it's all down to personal preference.
I just want to try this...
http://www.msfirefox.com/