I find the comment "Mark Levin is a really nice guy" to be very funny. A week or so ago, he had a guy call in who said "I'm a huge fan, I'd love to buy you lunch one day and have a chat," and Levin responded with "I eat alone." He's about as mean as any human being could possibly be, at least on his show he is. I doubt he's like that. However, he's very good at what he does. Medved is another guy who's really good at what he does, and he's about as mild as the Republicans come. Savage is decent, but he's wayyyy too angry and hateful for me to listen to him. And Limbaugh is another guy who's a great radio personality but a completely venomous jerk.
I'm a liberal but I can't listen to lib radio. Not because they're too mean, but because they're just not very good at hosting radio shows. Ed Schultz is an exception, he's fantastic and I don't think he's the least bit hateful. He's passionate, but you can always tell that he's lashing out at ideas and not people, and he says so much. Franken was a terrific host when he did his show, but I know he never really found his audience. Some of the debates he had with G. Gordon Liddy were absolutely legendary.
You also have to remember that older demographics are radio's primary target. Democrats who are really into politics are all about internet media and many of them don't even listen to the radio when they drive. Rush's audience is a bunch of retired couples and mechanics and truck drivers and that sort of thing. Those people will die soon, and talk radio will probably die with them.
And for fairness' sake, I'll mention that today I was listening to Levin and couldn't take it anymore, so I turned it to the Air America affiliate and the guy was talking about how he was excitedly anticipating Glenn Beck's death. On both sides of the aisle, these guys get paid for being vicious. And if you want really scary, listen to the armed radio network or whatever it's called on Sundays. The last time I listened to the show, they had a long discussion about when it would be appropriate for citizen militias to raid the White House and kill Obama and his administration. The consensus was "not quite yet."