The metric I like to look at when they include it is the "who did you vote for last time" question.
Granted, people can move between states, forget who they voted for, or simply lie to the pollster, But those numbers are another indication that the Colorado result is skewed towards the Republicans since the difference is beyond the MoE for the poll.
If one were to adjust the toplines to have the poll samples conform to actual 2008 results, you'd end up with: CO: O+2, VA: O+2, WI: O+7.
You can't do that. Poll samples on the "who did you vote for in the last election" question often don't match the previous results for various reasons - people who voted in the previous election fail the likely voter screen because they aren't as enthusiastic about voting this time or moved in or out of the state or died or have buyer's remorse about who they voted for the last time and lie to pollsters or whatever. The 2008 electorate isn't the same as the 2012 electorate.
That said, the CO poll seems a bit off. But I wouldn't doubt a small Romney lead. Obama is campaigning there today for a reason. The state is at least close, not some Democratic blowout.
Transposition errors are rare, but they happen. I would have been more likely to believe that Quinnipiac would have Obama up 5 in Colorado than down 5 when Rasmussen shows a tie and PPP shows a small Obama lead. If it is a transposition error, then Quinnipiac will correct it fast.
Checking it against the previous election is valid. If a state went 53-46 for Republican A against Democrat B in 2004 and a representative sample of those voters now goes 46-53 for Democrat A' against Republican B' in 2008 then something is very different.
Polls can do one thing reliably: show whether candidates are poaching what was recent and necessary (if perhaps flimsy) support of what might have been a winning campaign in recent years. One would have expected statewide polls to show such between 1976 and 1980 for reasons that should have been obvious. Carter was a disappointment as President who beat an incumbent who had been appointed to the Vice-Presidency after never having won a statewide election and Reagan had smoothed out his reputation as a hard-liner while becoming a slick politician.
In 2008 John McCain had a better life story.... but he faced a Democratic nominee far stronger than John Kerry in scary economic times. Barack Obama is as slick a politician as he was in 2008; he is a good strategist. If the economy is worse than it was in 2007, then expectations are also lower. Could it be that an effective leader successfully gets people to lower their expectations instead of promising the impossible? FDR did that; Jimmy Carter didn't.
All in all I can state that the Presidential election of 2008 will, barring unforeseen and unpredictable events or (now) unquantifiable effects of recent behaviors, look much like the Presidential election of 2008. In essence Barack Obama is in roughly the same position that he was in in August 2008 with far fewer ways in which to lose than in which to win.