I recently made the jump to Vista. I feel like I now have it tweaked and performing reasonably well. I can sit here and type to the sound of my keyboard keys and not to the grinding of my hard drive. Vista spent a lot of recourses just being vista and not doing anything useful.
I like to pull up task manager and see that CPU usage dance between 0% and 2% as I type this. I have a little blog authoring tool open and IE displaying my last search behind me. I also trimmed the memory usage down, but I cant get it anyplace close to XP or server 2003.
Most of my tweaking was done by disabling services to features that don't add any value. I have disabled everything possible that does not impact my use of Vista. I have some things enabled that I would remove if I did not VPN regularly. Here is my list of running services that I felt are required for a stable functioning computer.