I've been playing around with Vista Ultimate x64 and I'm very impressed. Considering how moderately to poorly Windows 2000 and XP ran on fast machines available at the time of their respective releases, Vista runs like greased lightning. I added a 1GB USB memory stick and enabled ReadyBoost and now Vista boots faster than Windows XP x64 (I dual boot)!

I was very skeptical when I first installed Vista, but pretty much everything about it is superior and that superiority starts at the initial install screens. The installer is way better and less reliant on user input than any previous Microsoft OS. I can't say I like the boot.ini replacement database thing (bcdedit), but considering it lets you run compressed Windows images as actual OS drives, it will probably grow on me.

Save for the lack of temperature monitoring and overclocking software available, Vista is worth making my primary OS.

BTW- Technet Direct subscriptions are an insane deal. Never buy retail again!