It really is the worst! I always give the pizza a few good shakes before I put it on the stone to make sure it isn't sticking. If it seems to be sticking then I gently add a bit of corn meal underneath the part that is sticking. This usually works. As far as cleaning up the mess, I would say use a spatula and scrape off what you can, then soak it for a while and have another go at it.
Best regards,
Tin Roof