I find the new VMWare Player release candidate performs much better than Virtualbox for virtualizing Linux on my hardware, at least.
It's worth a look-- the new version makes it essentially a mini VMWare Workstation (it supports creating VMs now, and has other niceties like Unity mode, Aero support on Vista and 7, and multiple monitor support). And it has guest additions (enabling seamless mouse mode, Unity, file sharing, etc.) available for Linux, unlike VPC.