I see two very plausible scenearios on the opposite extremes.
Negative – After cleaning up the online gaming scene, the DOJ and all state licensing organizations severely limit advertising and promotion of online games where money is won or lost. Requires strict compliance to a set of mandates, background checks and licensing agreements along with large fees for casino sites and affiliates. Goes after and sues violators (including affiliates). Facebook, google and yahoo dominate the scene.
(Long term effect – Only the ‘big guys’ can participate legally. Fosters a dramtic increase in international based operators with illegal games)
Positive – USA citizens can legally play online casino games of all kinds. Reliable casino sites are monitored for honest games, payouts and payments. Funds processing becomes simple and reliable. Affiliates continue to flourish and provide quality tips and information for the gaming public. Google is allowed to accept casino advertising but due to it’s dominance in the search engine market, it does not directly promote real money games itself. Facebook apps developers devise affililate programs to increase their market share in a competitive manner.
(Long term effect – Everyone wins. Shady operators have no advantage and close down)