Love it. I think office 2007 is a massive improvement over 2003. Speed-wise it’s fine for me on both vista and XP boxes.
2007 is much nicer once you start connecting lots of MS stuff together too, particularly sharepoint.
Gooner, if you’re using excel a lot, check out this pack of tools for excel..
http://www.asap-utilities.com/ , they’re absolutely fantastic and will help automate/speed up many of the things which should be easy by default.