
good news for Virtual Machine addicts : VirtualBox team has fixed issues which were preventing VirtualBox to work properly with GNOME Shell. You need VirtualBox release 4.0.8 (minimum) and GNOME 3 live image release 1.3.0 (it contains updated VirtualBox guest additions, required for openGL).
To download the image : http://www.gnome.org/getting-gnome/
Enjoy.