When I reformatted and reinstalled Windows, I was surprised with how much I didn't have to keep. My music was on a separate internal drive and other various places throughout the house (and on Google Music!), all my pictures were backed up to Picasa and saved on a portable drive, most games were steam games so that's easy, and most everything else is on some sort of Google product and stored in their cloud.
Google makes me so happy with the services they provide for free :D
