One issue I see already is that I don't foresee them having a way to vet every single entry to make sure nobody enters with multiple Twitter accounts. It's easy enough not to provide any real information unless you win, and although I respect that they tried to use Twitter to make entering open, easy, and overall low effort, there are too many loopholes to exploit that there is no way they will completely manage to deal with. It may seem more fair that those at PAX Prime can get three entries with the punch card, but in the end, it won't be much if somebody else enters with 100 Twitter accounts.
Granted, 100 Twitter accounts is obviously far more effort than the average person is willing to put in, but some people are willing to put in a lot more than the average effort for something like this.
