I also slide around a bit, it's REALLY annoying, especially when I wanna have some fun, and I slide back onto the passenger pad. When I manage to get it done, I'm having my seat reupholstered with a suede textured material. That oughta solve my problem.
Already mentioned, the Alaska Leather Sheepsin Co. should have a proper fitting cover for your bike's seat...it adds about 1/2" to the seat height but it's comfy and will keep you from sliding.
I don't want to be locked down on my seat. I slide around on it on purpose sometimes when cornering hard. It's a Mustang though, that and I grip the tank with my knees when I really need to be locked in.