IF by some chance, the electoral vote would be evenly divided 269-269, the House of Representatives, likely to have more states with a Republican majority delegation, would then get to choose the President, as they did in 1800 and 1824, and would then choose Mitt Romney, their party’s nominee.
But if the Democrats continued to control the US Senate, then Vice President Joe Biden would be likely to be chosen, and we would have a split White House, which we only had after the 1796 election, when Thomas Jefferson was the opponent of John Adams, and ended up as his unhappy Vice President, and then defeated him in a tumultuous election in 1800.
The 12th Amendment in 1804 was supposed to prevent such an eventuality again, but it is possible, but highly unlikely, that such a scenario could happen.
This would be bad for America, as certainly Romney and Biden would not get along, and it is well known that Biden has ambitions to run for President in 2016, and would likely oppose President Romney on every issue imaginable, as they might be opponents in 2016, when Romney would run for reelection.
It is interesting to think about this, but no one should worry, as the odds of a tie of 269-269 is highly remote, and every indication from the “swing states” and Nate Silver in the NY Times is that Barack Obama will win the Electoral College without any problem, and win most of the contested states, as many other polls also indicate!