Woo! The 3.1 beta is out (get it here), and it includes a huge performance increase: IF you enable it.
I’m going to try it out on digg.com — there’s a huge amount of ajax and js there. Comparing 3.0 vs. 3.1 (with TraceMonkey enabled) should prove interesting. The Safari nightly builds are amazing with Apple’s new js engine, so this should be enough to bring me back to Firefox full time now 🙂