It’s better than a beta, if not quite ready for prime time. It’s the Firefox 2.0 release candidate, all operating systems.
Some nice new features — a little prettier, a spell checker for the text area (great for us bloggers), better security, improved tabbing. I’ve been using the beta and have been pleased with the changes, though it does seem to crash on start-up too often (Mac !?!?).
There is big new security issue with Internet Explorer, so you might want to consider Firefox or the release candidate (Windows only) of Internet Explorer 7. It’s a big improvement over IE6.