My absolute favourite plugin LiveHTTPHeaders doesn't work with Firefox 2.0. I'll stick with 1.5 for the time being I think, or keep a version of Firefox Poratable around for those ever so important plugins.
http://portableapps.com/If you haven't discovered portableapps.com yet, take a look. Just the thing to go on your USB memory stick.
The BBC News website has a head-to-head comparison, which I think puts Firefox marginally in front.
http://news.bbc.co.uk/1/hi/technology/6086798.stmMy initial verdict is FF2 is pretty good. It's all those little refinements that, though initially irksome if you're used to v1.5, really make it worth the upgrade.
Jim