This is truly cool stuff. VHDs are no longer "just" a virtualization file format. They're baked into the OS. Yes, you can boot an entire OS from a single file. You can create a VHD from the Disk Management Console without having Hyper-V installed.

Devs will love it because it vastly simplifies testing on different OS configurations. Of course, you can do this with Hyper-V already with multiple VMs, but now you have the same goodness in a non-virtualized setup as well.

IT folks will love it, as it dramatically simplifies data center management. Instead of tracking which OS and what patches a machine has, you can just have a set of reference images (VHDs). Drop any number of VHDs on the machine, tell it to boot one of them, and you know exactly what you're running. Want to change to a completely different setup? Just point at a different VHD file and reboot. No need for separate disk partitions, OS reinstalls, etc...

Note that to boot VHDs natively without Hyper-V, the installed OS must be Windows 7 or Windows Server 2008 R2, but that's the expected price of progress. See the link for the exact details.

http://blogs.technet.com/virtualization/archive/2009/05/14/native-vhd-support-in-windows-7.aspx