The GNOME 3 FAQ states:
To get the GNOME 3 experience, you need hardware acceleration.
So, if you are looking to use GNOME in your virtual box, you have to enable hardware acceleration for it.
But, fear not. Developments are going on to make sure that GNOME doesn't have to rely on GPU hardware and soon enough, through LLVMpipe, you should be able to get GNOME experience in your virtualbox without having to enable hardware acceleration.
It's now possible to run the GNOME Shell with Mutter but not having to
rely upon any GPU hardware driver! Software rendering is now working
with GNOME Shell rather than any fall-back thanks to improvements with