It looks like VMware just released Fusion5, I currently run 4 and I find it a stable application. I think some of the new features, improved graphics and support for more ram are nice to see. I couldn't find any reviews as it was just released but I may upgrade in a few weeks if I start seeing positive comments on it. http://www.vmware.com/products/fusion/features.html
...and Parallels is going to version 8....just when I got them for a decent price with a bundle deal....
When you see Parallels in a bundle, that means that they are going to upgrade within a few months. Always, always happens.