I had an opportunity to meet Tucker Carlson on a radio show (long story on how we both ended up in the studio at the same time) and I got to listen to him talk and hang out casually. I had, at that time, only known him because of the John Stewart ass reaming he took. And I noticed, he really was sincere about his point of view. Him and the DJ were/are good friends and when they would go to commercial they would keep talking about the topic.
I actually like Tucker, even if I disagree with his political views. You can tell that he has thought things through.
I wouldn't say Beck believes what comes out of his mouth, but I do believe Hannity, Limbaugh and O' Reilly believe every word. They just happen to be reallllly good at pushing the right buttons and saying it in a way that adds the shock value. I will say this, they are very, very good at what they do.
I am not sure what to think of O'Reilly, but Hannity and Rush I have a hard time believing. I just can't picture a sane person saying the things that they say other than attempt to increase ratings. Hannity's obsession with "Obama is the "Messiah"" thing just baffled me.