You’ve been seeing a lot of virtualization specific posts recently here at Ubuntu Tutorials. I’ve been tinkering with a number of virtualization options, namely VMware Server, Virtualbox and now KVM with Virt-Manager.
I’m not going to go into comparing the three in this post, but I will say that KVM is the only solution that will let me run 64bit guests on my 64bit host. It also cleanly manages networking, whereas VirtualBox still has issues there. KVM is still fairly new however so the UI features are not as nice as the other two.