Currently running Firefox 0.8 - I'd like to say that it's faster than IE but actually I don't find much real-world difference. It's certainly nice to run something that is less vulnerable to security holes and hijacking. The real clincher for me is the tabbed interface, I just find it so incredibly convenient - no more windows scattered all over the place. But some web pages are not W3C compliant and don't display correctly in Firefox (or Opera) - this isn't really a big issue - just an occasional irritation. Have to say I don't use IE much anymore...