Just replaced the Boxster S on the trunk. Dental floss worked great in getting the old emblems off but man the residue was a pain. I tried goo gone, lighter fluid, wax remover and nothing touched it. I finally went to the Auto Parts store and got some 3M general purpose adhesive remover. I let it soak in for 3 minutes and the residue came right off. A half hour job turns into 2 hours.
The paint was faded where the old emblem was, so it was easy to see where to install the new one. So the moral to anyone doing this is get the right stuff for the job.