I'm running Unity3D in a virtual instance of Windows, using the Virtual Box software on Linux. I have guest additions installed with DirectX support. I've tried using Windows XP SP3 32-bit, and Windows 7 64bit. My host is Ubuntu 12.04 64bit.
I installed and registered Unity on both. It loads up fine, and then crashes my entire VirtualBox instance (equivalent of a computer shutting off with no warning).