It's already almost 2 months since I got my Mac and, while all other switcher installed a virtualization software as first thing, I'm still running on Leopard only. Probably because I still have 2 other laptop running on Windows at home (my old one and my work one).
But sooner or later I've to do it: but I've not decided yet what to install.
I'm leaning a bit toward Fusion. I found a very complete benchmarking that says Parallels is better than Fusion (even though Fusion is faster hosting Vista), but it compared Parallels 3.0 with Fusion 1.0 that didn’t have Unity as the current version 1.1, so the results are totally useless IMO.
In the meanwhile I subscribed to the blogs of both Parallels and Fusion:
Now that I submitted my Silverlight app for the INETA competition I'll have a bit more of spare time, so maybe this weekend I'll install Vista on BootCamp and then try the 2 virtualization solutions.