It's entirely possible on VirtualBox, but it requires you to have a similar processor to an existing Mac, and some additional wizardry. I can verify it works for some virtualization software through at least Snow Leopard...not sure about Lion and beyond (but probably).
I love VirtualBox and I think it beats VMWare and others in UX department anytime. That said, for running Mac (Hackintosh) I would STRONGLY recommend VMWare. On VirtualBox I have tried 3 (!) different images and they were all slow, while the one I am running on VMWare works properly. And I mean properly.
I never had these kind of problems with Linux and Windows guests on VirtualBox though, so I'm not sure what the problem is - but it is real.
