I was just thinking about how nice virtual machines are...and how even "rebooting" is less painful, because at the very least, you don't have to wait for your physical computer to turn off and on with all the mobo shannanigans at the start... so, what if I ran everything in a virtual machine? Then I wouldn't really need a primary OS, I just need something than can run VirtualBox or what have you. So what's the lightest weight OS I could install, that supports a good virtual machine?
You can use an enterprise linux like CentOS (libvirt, kvm, xen) or Debian with XEN. This way you can run your system virtually... however, you won't ever achieve the same performance. (Whether it be IO, graphical, etc. XEN/qemu/kvm is close to the IO perf, but still not the same. You won't have Graphical accel (normal) in your box, etc etc.)