Thanks for the correction and the link.
He's still never been naturalized, though, so he's still not a citizen.
If he became a citizen via naturalization, he would not be a natural born citizen, and thus he would be ineligible.
However, if he was born in Honolulu, then he was a citizen at birth, which is the definition of "natural born". And of course, he would be eligible.
If he was born in Mombasa, the fact that his mother hadn't resided in the US for five years after the age of fourteen would have caused him to need naturalization. In that case, he'd be a foreigner, since he's never been naturalized. And even if he had been naturalized, he'd be ineligible, since he wouldn't be natural born.
Now, John McCain, in contrast, was eligible despite being born in Panama, because his parents were both citizens. Indeed, in McCain's case it would be especially outrageous to question eligibility, since, not only were his parents citizens, they were abroad in service to their country when they had him.
To return to Obama's case, in order to make him ineligible, it's necessary to prove he was born outside the country. The other argument, that his stepfather gave up his citizenship by moving him to Indonesia fails because parents can't renounce their kids' citizenship. The kid himself must do it after attaining majority. Also, the fact that he may hold dual citizenship (in Kenya, Britain, or Indonesia) is irrelevant. Foreign law doesn't influence eligibility to be president.