I have a Hyper-V Windows 2008/Sharepoint 2010 VHD which I am dual-booting from Windows 7. Works great once the memory is beefed up to 8gb. However, during execution the VHD mysteriously expands to 132GB. After shutting down it comes back to a more reasonable(?) 55GB.
Might not be applicable in this scenario, but for those who want to shrink a VHD file without the Hyper-V manager, see above.