Many stickers will simply come off if you peel them off SLOWLY. Although, many seem to act like they 'have no time' to do that the right way. Also, though it may be an annoying tactic and make noise which will disturb other people, here's how to get that residue off without using Goo Gone(which I feel leaves another residue all its own).
Use the sticker you just removed gently and hold it in your hand and start re sticking it to the case, but as soon as it makes contact with the case, peel it right back off. If you do this quickly enough, you can get ALL or at least most of the residue off without using Goo Gone.