As a comment, I've been using Parallels 3 for almost a year now. It was adequate at first but tended to run more slowly over time. Using Windows XP meant a restart of it each time, as hibernating would slow it to a crawl upon waking.

I decided to install and run a demo of VMware Fusion 2. Granted they still have some development issues of their own but I'm amazed at how quickly and smoothly it runs. It's been a month of using it now and I feel converted to VMware. Both Parallels and VMware have or will have recent updates in Oct, and both are decent apps but when it comes down to which one I'll likely stick with in the long run, it's probably going to be VMware.