I’ve been messing with vms on the mac for the longest time. Ive always been disappointed with Parallels Desktop, it runs so slowly. I had a Win 7 VM, and it would literally take 10 minutes to start up on my Apple Macbook Pro 2.26 Core2Duo running OS X 10.6 and at the same time bring my computer to a grinding halt.
VMware Fusion 3.0.0, I just installed today and converted my Parallels Desktop 5 Win 7 vm to vmware, and now my computer still takes a while to load the vm, but it no longer kills my computer.
I definitely recommend VM over Parallels.