After installing the new Ubuntu Beta (Server edition) inside VirtualBox I was greeted with a very friendly "CPU Not supported" message from the kernel upon rebooting. It seems that VirtualBox does not support PAE and the Ubuntu server kernel requires it. Parallels has a nice knowledge base entry that addresses the same issue here. I followed the instructions and everything seems to be working fine now. It's unfortunate that the Ubuntu server kernel won't work but I suppose this is a fine solution.