+1 on using gentle heat (a hairdryer is fine) before peeling it off. Follow with a solvent for final cleanup. My favorite solvent for removing adhesive residue is 3M General Purpose Adhesive Cleaner. It's very effective yet safe on cured paint. Works great on grease, tar and other assorted goo. I've had the same quart can for nearly 20 years now and it's still 1/3 full. Most auto body supply stores carry it for about ten bucks.