I have been using VMware Fusion 2 since day 2 of purchasing my Mac for running Windows. I find it an extremely reliable and fast platform for running any virtual machine on Mac.
Recently MacTech performed an exhaustive set of benchmarks comparing Parallels Desktop 4 to VMWare Fusion 2 to run Windows on a Mac. They stated Parallels a winner in most of the tests (by 14% to 20%) compared with VMware.
Cool, but I am not buying. I won’t switch reliability and flexibility over that 1-2 sec speed advantage anytime.