Both, Ubuntu 12.10 and 13.04 perform very slow when running in VirtualBox 4.2.12.
How do I run Ubuntu with unity or enabled transparency smoothly with VirtualBox?
Graphic/performance fix for Ubuntu was tested with Ubuntu 13.04, 12.10, and 12.04. Part of this solution applies where aero / transperancy is used including d3d games.
Recommended graphic memory or virtual ram for aero based operating systems is 256 MB min.ram -768 MB for 13.04
Virtual machine settings
Reference and sources::
babarehner @ e-wrench.com and youtube
sanct on http://ubuntuforums.org/forum.php
rpxmac on forums.virtualbox.org
Related questions on Ask Ubuntu
Make sure you enable 3D support on Virtualbox, and on guest Ubuntu virtualbox setting. Also give your virualbox enough RAM and cpu cores. Having dedicated VGA will help virtualbox performance as well. How to fix slow performance ubuntu 13.04 running in virtualbox
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