I'm using Vista Ultimate right now. (I did not buy it.) I haven't had any problems with it, but it seems that a dual-core CPU is way better for it than a single core, which is what I have now. When using a game (Even Halo: CE, which is not exactly "New"), and voice chat on MSN at the same time, the chat tends to skip and jump a lot, and repeat words for some reason.. although, I did fix this by upping the priority of msnmsgr.exe, but the even the game stutters occasionally due to this.
When not voice chatting or using WMP, though, games do run _faster_ than in XP. For example, XP, I was unable to raise the resolution in FEAR above 1024x768 to 1280x960 in maximum settings, otherwise I'd average around 20-30FPS: In Vista, I achieve this and run at an average of 50FPS. Unfortunately, because Vista uses more memory, I cannot use maximum texture resolution without the game stuttering over and over each time I reach a new area. (Athlon 64 3500+, 1GB DDR2-533 RAM, Geforce 7600GT oc'd to 700/801Mhz).
In terms of none-game performance, it runs faster than XP on the same machine, even while using Aero.
I am hoping they'll do something about the DVD/CD burning, though. It works fine, but its just confusing. the same goes for the disc defragmenter, no longer do we have the good old "This is how many files are fragmented" and the progress bar, instead, we have a box saying "disc defragmenting". That's it. It says it's defragrmenting, but it doesn't tell you how much is left, how much is fragmented, etc. I miss the old one.
Oh, and it takes longer. Much longer.
Disc cleanup is faster, but seems unchanged compared to XP.
Whee!!1