Did this months ago, on my old Pontiac. ***This does work*** Of course, my stickers were very old, but with one of those long cheap blades out of one of those plastic box cutters, and some WD-40, I got all of those bumper stickers off!! Also, you can use it to help remove the emblems off at the salvage yard too!! :-)
http://www.youtube.com/watch?v=O3z4l1ylMcs