Have you ever gotten your system to a state that you absolutely love - all your apps and utilities loaded, Visual Studio instaled, etc. - and find that you need to load Potentially Deadly Beta Software v0.8? Have you ever cringed at the thought that loading such software runs the risk of screwing up hours of work getting your machine configured just right?
Enter disk2vhd. Those crazy SysInternals guys, they are wicked smart. This free (!) utility can convert the drive that you are currently booted in to into a VHD. Once there, you can do all kinds of fun stuff. Load it up in Hyper-V. Configure Windows 7/2008 R2 VHD boot with it. All sorts of stuff. Load Deadly Beta Software on it.
Just generally go crazy.