When I first read that Sun’s xVM VirtualBox included Microsoft VHD format support, I booted up an existing Windows VHD I had and started through the fixup process – second boot of the VHD and it was pretty much corrupted. I just tried again with version 2.1.0 and had the same problem (luckily against a copy of the original VHD). Somehow I haven’t had the issue on my Linux VHDs – go figure!
The issue has been visible for a while – see: http://www.virtualbox.org/ticket/2541
I hope that this is addressed - when compared with VirtualPC 2007, VirtualBox seems to run images with better performance and of course the Sun PUEL release has USB support.