I've always found naphtha lighter fluid (the kind you'd use to refill a Zippo lighter) to be the best thing for sticker residue, on book jackets and other things. Ronsonol, in the flat yellow squeeze bottle is the most common brand here in the States. It's never damaged anything that I can remember. I'd advise against acetone. It's a wonderful solvent but it will quickly dissolve many plastics and finishes, so a stray drop can do serious damage.