I have personally used this product several times. Worked great first time, every time and left the paint untouched.
http://www.autozone.com/autozone/acc...er=189453_0_0_
I have seen other friends use what amounts to a giant rubber eraser spinning on a die grinder. The friction of the rubber against the vinyl and then the adhesive removes all traces of the decal.
http://www.amazon.com/gp/product/B00...d_i=B001DUT3Y0
Neither method is inexpensive, but they are quick and very thorough.
Goof-Off works well on the decal residue but will dissolve paint also.