It is up to those who claim he is not a citizen to prove it. Obviously, they have not if he's still in office and there's no larger-scale investigation, etc.
Otherwise, the conspiracy theorists should give it up and move on. Jobs have gone poof, the housing market still sucks, the government might shut down in like two weeks, we have a budget to cut and where to cut is the driving issue, and there's foreign affairs to keep an eye on.
Put out PROOF, not just "why I think he's not" or shut up and focus on the issues that could weaken/divide this nation faster than "is Obama is citizen or not?" ever could.
I will say that I agree with the person that found it shocking that it is not required to even enter the race, even at the primary level.
That's the one thing the theorists have brought to light, and SHOULD be dealt with. Everything else is just conspiracy and guessing with no facts to back it up - or else it would have run with real legs by those with real power.