I run Vista Ultimate at home and frankly, hate it. It has some cool eye candy and such, but it is very quirky. Things that I hope they fix with this SP:

Inability to log off users. I can't log a user off, I can switch just fine, but if I want to log off a session, the only way to kill it is to reboot. Very annoying.

Updates that won't install unless you are powering down: WTF? Seems that I always have a nagging update or two that ONLY install on system shutdown. Very annoying.

Mystery of the vanishing printer. My HP laser printer sometimes just dissappears... Then it has to be re-installed from scratch. Very annoying.

Fleas: My dog has fleas, and I am pretty sure Vista is responsible. Hopefully this service pack will take care of that too.