Ed Kilgore's spin:
There are two big takeaways that Democrats must understand from the enthusiasm gap data. The first is that it's a mistake to primarily assign turnout disparities to an insufficiently progressive agenda from the Obama administration. Maybe a different agenda would have been a good idea on policy grounds, or might have had a different impact on the congressional dynamics. But there's really little evidence that the discouragement we see among progressive elites is that widely shared among rank-and-file Democratic voters, whose relative likelihood to vote or not to vote is more easily explainable by structural factors.
Second, Republicans may be benefitting today from the hyper-excitement of its radicalized conservative base. But they will pay a price in the long run for the sort of agenda and rhetoric they are being driven to. That will become immediately evident in the 2012 cycle, when GOPers are forced to disclose their extremist hopes and dreams for the country, in the context of an electorate that is automatically less favorable.