In 2000, George W. Bush's <a href="http://archives.cnn.com/2001/ALLPOLITICS/03/11/palmbeach.recount/">winning margin in Florida (and thus the presidency of the United States), was 537 votes</a>, in an election whose legitimacy is still hotly debated (and to me, will never be legitimate). The hanging-chads issue alone could have swung the election to Gore by thousands of votes—just one among many irregularities. But in any case, it was close enough that it was possible to steal.
Years ago, I managed a friend's campaign for local office; he was declared the winner by seven votes, and in the recount, his margin of victory slipped to four.
Four votes determined that election. If just five more people had shown up up to vote for his (entrenched incumbent) opponent, he would have lost.
Of course, it's not enough that every vote counts. Who counts the votes is also an issue; witness the calamity in Iran.