Most of Limbaugh's audience, of course, listens to him, not because they agree with him, but because he agrees with them.
He hasn't changed many people's minds, I'd guess. Not that he needs to. Personally, I started listening when my sister strongly recommended him. I thought, great, last thing I need is to hear a bunch of people ignorant of what's going on, calling in to expound on what's going on. I'm plenty ignorant enough, and I don't need more of it. But I tuned in, just to see why my sister was so up on him.
When I found the station on the dial, I heard a man talking about racism, and more importantly about DESCRIPTIONS of racism. He was saying that one reason a lot of people don't like the Democrat party, is that they annoyed when they hear themselves called "racist" when they're not, called "bigoted" when in fact they never pay attention to someone's race or color.
That got my attention. I had never heard such a sentiment expressed on the air. Only descriptions of this racist or that one, how much "we" owed minorities, how oppressed they are, etc. The idea that most people are NOT racist, though I knew it well, had never been expressed in a public forum that I'd heard.
Limbaugh didn't convert me to any new ideas, or to anything I hadn't previously believed. Rather, I simply found him saying things I'd always agreed with... things that had never been aired where I could hear them publicly.
Presently he has some 20,000,000 listeners. Sounds like a lot, but that means there are 280,000,000 Americans who DON'T listen to him. I mentioned him to my mother at one point, and she said she didn't bother listening to him because he was way too sure of himself, "conceited", she finally said. Not a surprising reaction - Limbaugh is VERY sure he is right, and couldn't run a radio show as he does, without it.
My point in mentioning dear old Mom, is to point out that there could be a number of people who agree with Limbaugh's sentiments, but who don't like to listen to him.
As mentioned earlier, most Americans are conservatives. That is, they live their lives conservatively. The pay their bills on time, pull their own weight, and don't expect their neighbors to pitch in and help them. They contribute to charities, and DO help their friends and neighbors when they need it, but frown on anyone trying to FORCE them to do those things... just as they frown on the idea of their neighbors being FORCED to help them, even when they need help. They are, in a word, conservative. And most Americans are that way.
That some of these people turn around and vote for politicians who promise to do exactly that, through liberal tax increases, welfare programs, and government-coerced "spread the wealth" programs, is an enduring mystery. These are people who would never steal a dollar from their neighbor themselves, but who have no problem voting for politicians to do it for them.
Many have drunk the standard Kool-aide of "Conservatives are terrible, heartless, and evil, and Limbaugh is the worst of the worst of them". To a man, they have not listened to Limbaugh, but simply take the word of those benevolent politicians that it must be so; and so they stay away.
There's a great pool of conservatives out ther who currently don't vote conservative. Some of them don't because they have noticed that no conservatives have run for major office in the last few elections. Others don't because of their Kool-aide beliefs. But all of them can come out for conservatism, once they see one with the amount of media backing Barack Obama got, combined with the conservatism of a Ron Paul with a little common sense mixed in.
Only problem is, it's going to be a LONG time before the former shows up, and an unknown amount of time before the latter does.
Modern liberalism has peaked. We will never see a modern-liberal candidate get as many votes as Barack Obama did, ever again. Whether we start seeing a conservative (i.e. a smaller-govt, freedom-and-personal-responsibility avocate) do it, remains to be seen. First we have to find one.