[jerros]

I've seen guys on youtube get their old factory grips off the bike by using an air compressor and shooting it under the grip on the motorcycle. This makes the rubber grip balloon out far enough that it either breaks the glue or gives you a little extra room to get them off by using something like a screw driver to dislodge the glue. It takes a little time but looks to be the easiest way to get them off.

http://www.ehow.com/video_4974611_replacing-motorcycle-hand-grips.html