Michael:

If you've only seen whispering about the issue, I'll presume you missed the front-page story devoted to the topic in the New York Times. Go read it - it should clarify the issue for you.

But wherever you come down, I think you'll have to admit it's not going to make a difference. The only way to enforce the provision is to convince a federal judge to intervene. I suspect that any federal judge is going to decide that the issue is sufficiently well-known that the constitutionality of McCain's claim to being a natural-born citizen ought to be left to the discretion of the electorate. Federal judges are, as a class, extremely loath to intervene in electoral contests when it's not strictly necessary.

There's even an instructive precedent: in 2000, a federal lawsuit alleged that both Bush and Cheney were citizens of Texas, violating a constitutional provision requiring that the POTUS and VP come from different states. Cheney countered that he had moved his residence back to Wyoming more than thirty days before the election, meeting that state's threshhold test for citizenship. I happen to think that claim transparently false - there was no sense in which Cheney was still a resident of Wyoming and not of Texas. But the judge declined to intervene. I suspect that, whatever the legal merits of the objection, the judge decided that in this day and age that provision was best left to the electorate to enforce - who wants a federal district judge dictating the candidates for the highest offices in the land? So long as there's grounds to argue the point, they're better off not intervening.

The Constitution does not say you have to be born in the United States. It says you have to be a "natural born citizen".

McCain was a citizen as soon as he was born.

Why do you think that "natural born citizen" means "born in the United States"?

Before you answer that question, please be aware that the first Congress, composed (to a large degree) of the people who actually wrote the Constitution, explicitly defined "natural born citizen" to include people who were citizens at birth, regardless of where they were born.

Since when does the constitution require that the P. and VP be from different states?

And you are a natural born American if you are born of American parents anywhere... its up to different countries to decide how that works - but sometimes you end up with a minor with dual citizenship.

Minor point of correction: the Constitution doesn't prohibit both the President and Vice President from being from the same state. It merely prohibits electors for voting for two people from the same state. And so no party since has nominated two people living in the same state (although there was some discussion in 1980 of Ronald Reagan choosing Gerald Ford as his running mate; the fact that both were, at that time California residents effectively shot that down). But there's nothing constitutionally that would prevent two such candidates actually being elected.

From Amendment XII:
The electors shall meet in their respective states and vote by ballot for President and Vice-President, one of whom, at least, shall not be an inhabitant of the same state with themselves;

Given how close the 2000 election was, had Cheney somehow been ruled as a Texas resident, the Texas electors presumably would have voted for Bush for President, but someone else for vice president. Had they voted for Joe Lieberman, he would have become Vice President. But if they voted for anyone other than Lieberman (which would be more likely), then the Senate would get to vote on the VP. Again from Amendment XII:
The person having the greatest number of votes as Vice-President, shall be the Vice-President, if such number be a majority of the whole number of electors appointed, and if no person have a majority, then from the two highest numbers on the list, the Senate shall choose the Vice-President;

(Emphasis added). It's almost identical to the text governing the selection of the President, except that the Senate breaks the tie instead of the House of Representatives (voting as blocks by state).

The 12th amendment was passed to solve a larger flaw in the presidential election process: prior to its passage, the President was the person getting votes from the majority of electors with the highest total (each elector could vote for two people), and the VP was the person with the second-highest total of electoral votes. This worked well enough until 1800, when the new parties each nominated specific Presidential and VP candidates, and then the Democratic-Republican candidates Thomas Jefferson and Aaron Burr tied at 73 votes in the electoral college, requiring a vote of the House of Representatives to decide the presidency.