I'm a Windows System Administrator and I use VMWARE Fusion on my Core2Duo iMac and Air when I work from home. (Shhhhh don't tell my Boss.) Anyway they both seem to run VMWARE as quickly as the machine (Toshiba - i5 laptop) I cloned.
My point being, why all the people saying quad cores are needed for vmware and parallels?
Good point.
I guess this depends very much on WHAT and HOW much you are working inside the VM. For a remote desktop you obviously won't need so much power. But when running more resource hungry stuff you'll reach limits of a single cpu VM pretty quick ... I for myself run OSX plus a 4-cpu Windows 7 VM on a Mac Pro for work. the VM is running all day long in parallel to OSX. the workflow is awesome. BUT, it takes it's power ... thus, awesome setup on a 8-core mac pro, but on my 2007 MBP it's sometimes a pain ... ;-)
thus, 4+ core is very welcome on the laptop ...