Recent opera-related disagreements with Jonah aside, I think this argument he highlights as explanation of Air America's tumble into bankruptcy is pretty sound (conclusion, of course, excepted): The liberal radio market was actually quite crowded, mainly due to the overwhelming popularity of NPR. The impacts of Pacifica and so forth strike me as quite small, but radio wasn't a wasteland for lefties before Franken and Co. signed on -- indeed, nearly every liberal I know listened and listens loyally to NPR. Hell, half of them own NPR gear. And very few of them were looking for something more pugilistic, sharp-edged, or even exciting to replace their beloved public stations.
But nevertheless, liberals looked around, noticed that no one on the left precisely matched what Limbaugh was doing, and sought to fill the apparent vacuum. As Jonah writes, "That's why copy-catting the right is such folly for liberals across a wide range of fronts. They don't understand that they already control universities, for example. But they see conservative success with think tanks, so now they're investing in think tanks." Putting the think tank and university examples aside, that's mostly right. The conservative movement has stumbled towards a political infrastructure that works for them. The nascent progressive movement is trying to replicate a structure that works for conservatives. That's not necessarily the path to take. Liberals need to create a failure-accepting and chaotic funding structure that allows them to develop the sort of vast left-wing conspiracy that's well-suited to and popular among the left-wing.
Clarification: To be clear, I don't believe that NPR is liberal, I believe liberals listen to NPR. The two are not the same.
Update: Marc Cooper has some much more informed, lengthy thoughts over here. And he's right: I'm very earnest, very nice, and very ignorant about radio.