I use VPC to run Windows 2000, on which I run Outlook, Oracle client and other software development activities. It runs very well... then again, I don't run anything graphically-intensive.
(Yes, I have Entourage, but Outlook/W2K/VPC runs circles around Entourage. And there is no Oracle client for Mac OS X. I wish there were. All of our Java and Swing apps work fine in Mac OS X.)
edit: Forgot to mention: The coolest thing about VPC is being able to back up the entire virtual machine to a DVD-R and store it, or even move it to a different computer. The whole thing! And it's sure to work too.