Romney's going to win and win big. Independents won't fall for that shit again.
It was a fragile alliance that won the election for Obama in 2008, despite that he
out-spent McCain by a 4-to-1 margin.
Mostly it was a surge in support among blacks (88% supported Kerry in 2004, as compared to 95% for Obama in 2008), which alone accounts for half of Obama's 5 million margin in 2008.
Along with a surge in registration of voters under 30 in 2008, and a small margin of support among independent voters. Many of these, as you say, will be either voting Romney or just staying home in 2012.
Obama is currently spending insane amounts of money on negative ads in Florida, Vrginia and Ohio to turn the tide, but I sincerely hope that Obama's ship has already sailed. Certainly among independent voters (53% in the current poll support Romney), Obama has lost that support.