Comment 9 for bug 727410

Nope. We updated LTSP in Edubuntu and Ubuntu alternate to use the same default session as the server.

So if you have Unity install on the server (default for Ubuntu desktop), it'll try using unity for the session.
This works fine with most 3D capable hardware as long as the check in compiz/unity properly detects if the hardware is indeed 3D/AIGLX capable and does the fallback to 2D gnome if it isn't.

IIRC this bug report is about the VirtualBox video card driver not working properly with unity when the X server is remote. There should ideally be a test for that which would succeed on intel hardware (where it works properly even over the network) and fail on the virtualbox video driver.