I used it temporarily and it managed to mess with Vista so bad that everything reset to Internet Exploder on it's own, and refused to find Firefox at all until I removed 3 and reinstalled 2. It also, iirc, broke a bunch of pages that validated as strict CSS 2.1 and XHTML, which didn't make much sense, since that should've been one of the first things implemented (or in other words, taken directly from 2).

I'll definitely be looking out for the stable release, though I desperately hope they clean up the new drop-down on the URL input... twas ugly and made it extremely hard to find pages I wanted without just typing them completely in.

As for Vista... It's just like any other new Windows release. Looks nice, works acceptably, and if you don't have three times as much memory as last year, leaks it out like a sieve and needs to be rebooted constantly.