You really need to specify which type of virtualisation software you want to discuss. I was all set to vote and post some long comments ... but then realised you were only discussing host-based VM software (VMWare Server/Player/Workstation, QEmu, VirtualPC, etc). That's so blase.
Now, if you want to talk about hypervisors (Xen, Linux-KVM, VMWare ESX) and other lower-level VM software (and hardware), I'll be all over that.