I've thought about this a lot of times, but I know I'll never have the knowledge (or courage) to do it. What stops someone from handing the gate agent the boarding pass, waiting a little bit and then just walking out? I'm sure you could come up with some kind of excuse, but I haven't put that much thought into it. I doubt they remember you even 5 seconds after they scan your pass.

I am sure there is something preventing that... I know I am not the first one who has wondered about that possibility and I am sure some people have tried it before.