Don't do it at a dealer. You know that's just a rip off. Doing it outside will cost you half as much or less. It's just a protectant layer for your car. It does work though. The car isn't necessarily that much shinier (little bit, yes), but it is a lot smoother. It can be hard to throw a towel over your car b/c it'll just slide right off.
There's a company called CrystalGuard that makes a similar product. But, they have a Quick version that is supposed to maintain the coating of a professionaly done application, but can be used on its own.