heat gun (or a hair dryer) and a plastic razor blade will get most off. Then use a gel coat safe glue remover product like 3M makes to remove the residue. 3M also makes a remover disk that you put in a drill.
You will probably need to buff out the area to get rid of the ghosting - Finesse It works pretty well for this.
Hairdryer and denatured alcohol to remove adhesive.
I've used alcohol to disolve adhesive after removing vinyl lettering and found it much faster and neater to use than WD-40. I bet cheap tequila would work too :grin:.