I have been using VirtualBox VMs under Ubuntu for some time now, and, with the guest additions properly installed, the VMs always had 3D support - at least enough to run Unity in Natty.
But, when I've upgraded to a new machine (Dell Precision E4600) it no longer works. :(
The old machine (Dell Latitude D630) has Intel graphics, I think, and the new has ATI graphics, so that's probably the issue. I'm not sure how to find out what model exactly.
The host OS, Ubuntu 11.04, does have working 3D. That is to say, I can run Unity fine, glxgears works, and FoldIt also. Somehow it just seems to be insufficient for both VirtualBox and VMWare Player.
I did initially try to install the ATI proprietary drivers (through the Additional Drivers tool). They did permit 3D to run in the VMs, but they also caused lots of trouble with multiple monitor support, so I uninstalled them.
Have I somehow broken the default driver when I installed the ATI drivers, or does it just not support my hardware well enough for VMs? Might the situation be improved in 11.10?