Really? We use 2 free ESXi 4 boxes at work with 8 cores each. I don't think we can assign more than 4 cores to a single VM, but oh well.well, free VMWare is limited to 4 cores.
to me, that makes the decision......
In other news, I use Debian Squeeze AMD64 w/ KVM at home. Virtualizing my Amahi box (Ubuntu 12.04) and a PBX in a Flash box for a full VOIP PBX.