I once installed new Nvidia drivers on my Asus board and absolutely messed up the IDE so badly that I couldn't get an optical drive to work using DMA. I uninstalled, reinstalled, got new drivers, got old drivers. For two days I kept trying different things, read everything I could find, decided to kick the thing out the window. Then I tried going back to a restore point from before I installed the drivers. Perfect. I couldn't believe it.
That said, my friends asked me to come over one day because of messages that their drive was filled. This was like a 30 gig drive and they didn't do any video or audio or anything. I mean, they couldn't have had more than 10 gigs on the whole drive, but it sure was filled up somewhere. Yup, I turned off system restore, deleted all the restore point crap, and freed up over 20gb.
Apparently there was some weird situation caused by them upgrading from 98 or something because most of the restore points were all around the same time. Very strange.