Okay, today there was a nice announcement on heise… “Open-source competitor takes on VMware and Co.”
So we have an open-source virtualizer now? Yes we do 
The test on the page showed that it’s only a bit slower compared to the other mentioned virtualizer, so I gave it a run and it worked okay from the first moment. Stats indicated that there were some binaries around but we don’t like binaries if we can get the source, right? 
I’ve put a masked live ebuild in the tree and in fact we’re the first distro that has virtualbox in the official repository. So give it a run if you want to see the power of open source
There are good docs available on the homepage but if everything fails, you can stop by in #vbox on freenode (upstream irc channel)