When I built a new PC a few years back I bought my old Vista PC to my mothers house and left it there. I had tons of stuff on it: video clips, pictures, music, and tons of software i installed over the years. But after moving to a fresh install of Win 7, I didnt miss even a small fraction of what was installed on my old PC. But me being me, a data rat packer, I couldn't give up or wipe the Vista install when I recently wanted to repurpose the old PC. So I uninstalled all of the games, shrank the Vista partition, did the registry hacks, uninstalled all of the hardware drivers and did a block level copy using Linux and VboxManage to a virtual disk image on another hard disk. I then moved that image to my desktop PC, created a VM in Virtualbox, pointed it to my image and it worked! So when I need my old desktop I simply open up Virtualbox and run my old PC image. Though I will admit the first few tries failed to boot. It wasn't until I read about the registry hack to change the disk controller to a generic intel controller did it finally work. Then I did the same to the XP PC's at the family business as I was confident in the procedure. I saved money by not having to buy new Windows licenses and had a full Linux install to work in if need be.
Most of my Linux tinkering is also done on a VM running on my Win 7 machine. Since I still game from time to time, running Windows as the primary OS makes sense. Dual booting is so 2000's. No one should be doing it unless they really need the GPU under Linux and need to run Windows natively.
Virtualization is amazing. I cant wait until desktop virtualization becomes mature enough so I don't have to install an OS directly on the hardware. I just want a small thumb drive to hold and boot the hypervisor or the hypervisor is part of the BIOS/EFI. Then run and install OS's from there while being able to give them direct access to hardware if necessary and sharing the GPU. No more hellish driver problems. I can move the image or hard disk to another PC and run the OS. If MS were smart they would make a downloadable Windows image that ran right out of the box, like vmware player. Would make a hell of an option for mobile users: unplug the disk from your PC, plug into laptop and hit the road. when you come home and need more horsepower you can plug back into the main PC.