Yeah, I've used both. Started using Parallels of course because it was out first, then moved to Fusion when it came out. Actually bought Fusion as soon as the beta came out and I could pre-order. At the time I was having increasing amount of problems with Parallels, and I've been very happy with Fusion since. I'm not saying there's a huge difference between them and most users could probably pick either. One thing I like is that VMWare has a very long experience in virtualization and that there are tons of
virtual environments available for download for Fusion.