Question about OnLive service

I read about how to run games at 720p on OnLive you must have a 5meg internet connection, but if you have a 12meg connection how high resolution will you be able to run games?

I don't know, they haven't said anything about that. Though it's definitely possible that you could then run game at 1080p, or something like that with a connection that fast. But for the time being, all it means it that there won't be any latency while using the service. Hopefully this question will receive a proper answer sometime soon.

720 will still likely be the max regardless of the speed on your end. It costs them more money in bandwidth to send you beyond 720. So they aren't likely to do it.