I say somewhat interesting, because if it actually came to the forefront, I can't imagine them ruling him ineligible, especially if the Republican Supreme Court has the ultimate decision, but there's apparently a bit of conversation regarding John McCain's eligibility to be president.
The issue is that he wasn't born in the United States, but rather in the Panama Canal Zone while his father was stationed in the area by the military. The Constitution has a provision about "natural-born citizens" being the only ones eligible for the presidency. Some believe that means that only people born inside the United States are elegible to be president. Under the strictest interpretation of this provision McCain may not be eligible.
First of all, I don't imagine that anyone would challenge McCain's eligibility, nor, apparently, is it very clear who or how a challenge would be raised. Secondly, McCain has never been anything other than an American citizen, which is enough for me to end the conversation. The provision has never been challenged, though it seems pretty clear that a naturalized American citizen, say the Governator or Madeline Albright as examples, would not be eligible under any interpretation, but I can't imagine that McCain would be deemed to be ineligible.
Still, it's an interesting question. This seems like something that's screaming to be clarified by an amendment to the Constitution, but good luck with that.