lets put it this way. The builds i tested were.....interesting to say the least, a lot of cool features in theory, but during my testing (build 5456 was my last vista DL) wireless was super buggy, and the anti-virus didnt work at all (either that or the libraries were super old). The firewall worked great though, but i assume its based off XPs firewall.
Really thats my only negatives for vista. Some newer games didnt work, but i assumed it was because vista was in beta. Id have to test CS:S/HL2 and Quake 4 a run, as well as photoshop, flash and zend before i give my thumbs up to vista. Dont worry, already got a copy from work, and it will be on my new machine.