Seth Masket, an associate professor of political science at the University of Denver, calls Colorado "an interesting case in that it has not been a swing state that long. Colorado was relatively safe for GOP candidates up until decade ago." That changed, Masket said, with the influx of Democratic-leaning migrants from the West Coast, many drawn by the high-tech jobs in the metro Denver area. "The political geography of the state is pretty fascinating. Boulder and Denver are quite liberal, while Colorado Springs is very, very conservative, and the west is slightly libertarian."
The state that put Obama over the top in 2008 could do the same in 2012:
A simple yet meaningful way to look for the decisive state is to order the states according to the winner’s margin of victory. By arranging the states in this way, we can find the cut-off point where the winning candidate crosses the 270 electoral vote threshold. The state that gives a candidate a majority of the 538 votes in the Electoral College is the decisive state.
In 2008, that state was Colorado. Obama won the Centennial State by about nine percentage points over John McCain; had Obama failed to carry Colorado and every state that he won by a smaller margin, the Electoral College result would have been a 269-269 tie, a result that would have thrown the election into the House of Representatives.
Bloomberg explores all the swing states and finds their economies doing better than most, hence the solid Electoral College lead in a tight race.