Just Randomly

Assuming that the overturning of Proposition 8 is upheld in the federal courts, by the end of this year, 23.3% of the American population will have the right to wed their chosen partner regardless of gender. This will include the two states that represent the largest economies in the country. That being the case (and the very real possibility that several more states will establish similar rulings in the next year), while a federal version of the law will not be put forward before the 2012 elections, there will be a ruling that finds laws which allow individual states to not recognize same sex marriages performed out of state as legal are unconstituitional.

Historically, that's the tipping point. As Loving vs Virginia effectively ended any ability to enforce anti-miscegenation laws, the sheer numbers and mobility of Americans will force a similar challenge to the Supreme Court sooner than later.