Use a hot air gum, like a hair dryer. Start at a corner to peel. Apply heat, then slowly peel the label off. For final clean up of the residual goo, I use VP&P naphtha (evaporates faster than mineral spirits). With ABS and most other plastics, it doesn't hurt to add 10% toluene or xylenes. With polystyrene (like CD jewel cases) any stronger solvent will cause fogging. Even with the cheapest polystyrene, naphtha may cause a little fogging. Butter is even milder as a solvent, but needs to be cleaned. You can also use another piece of tape (my favorite is 3M making tape) to remove the goo. Add the tape. press it on, strip off quickly. Repeat as needed.