John Heilemann thinks it could happen:
Please do not dismiss the possibility, because for all the confidence that Team Obama has right now about getting to 270, they are palpably nervous that Romney might still emerge with a higher national raw vote total than their guy does. This is not just a matter of the tightness of all the credible national polls; it goes to the difference between now and 2008 in the non-battleground states.
As Plouffe pointed out to me yesterday, Obama's popular-vote margin last time was inflated by the organic enthusiasm for him in deep-blue states where the campaign spent no money on advertising or organizing. This time, however, that enthusiasm does not exist to anything like the same degree, and so Obama's margins in places like New York and California will be pushed down — even as the organic anti-Obama fervor in deep-red states will be greater than it was in 2008, depressing his popular-vote performance even more.
Sam Wang, on the other hand, recently calculated that a split decision is very unlikely.
The Dish 