My impression is that Colorado is just about dead even. I'd be very surprised if either candidate wins by more than 4%.
Early voting numbers show more republicans voting than democrats, but there's no doubt that independents will really decide the race.
Among registered voters here, there are about 1,150,000 democrats, and 1,157,000 republicans (a difference of only 7,000), but 1,293,000 registered unaffiliated - more than either party.
Most of the early voting this year has so far come from mail-in ballots, which is the easiest way to do it. Republicans propbably enjoy an advantage there because many of the Obama supporters from 2008 failed to cast ballots in the 2010 off-year election and fell from the mail-in ballot rolls. So those folks, like first-time voters, will have to visit early voting stations in person or else vote on election day.
So, it largely depends on the Tuesday turnout and what percent of the Obama voters from 2008 get out to vote again.
In that regard, I've got a feeling that the saturation bombardment of advertising from both sides that we've seen here might tend to increase turnout. But who knows?