One of the first arguments I saw that Fox News was biased was a survey I saw on a website from some time in late 2003. It made an interesting argument: it compared beliefs held by Fox news viewers about concrete facts to beliefs held by NPR/CNN viewers about those same facts. The survey showed that people whose main source of news was Fox were more likely to believe incorrect statements that were flattering to the Republican party than viewers of NPR or CNN. For example, the survey asked something like "Does world opinion support the war in Iraq?", "Have WMDs been found in Iraq?", and (I think) "Is there a connection between Iraq and 9/11?" The correct answer to all those questions, backed up by evidence as strong as pretty much any historical record, is "No." But Fox news viewers were more likely, sometimes twice as likely, to answer "yes," which in every case makes the Republican party look better than a "No". (I won't bother to quote it all here, but for details, watch "Outfoxed". I can lend it to you if you want.)
A couple weeks ago, a right-wing friend of mine was skeptical when I told him that Fox was biased. When I told him about the survey, he said that he's never seen anyone on Fox say any of those things. So I asked, "Well, there's a relationship, there has to be some reason. Do you think [it's because] stupid people watch Fox News?" At which point he pushed me, of course, because he watches it.
Of course, I don't really think that people on the right are stupid. Or at least I didn't until I saw this. Just now I was reading dailykos.com and found this article. The details of this new survey can be found here. To summarize: the majority of Bush supporters hold incorrect beliefs about his positions on several issues, like banning land mines and the Kyoto treaty and many others, and the proportion of Bush supporters misinformed about him is much higher than the proportion of Kerry supporters misinformed about Kerry.
Dammit, I want to be fair. I want to believe that people are basically good and the only serious sticking point in this country is when differing values. No I still believe it, I know plenty of admirable right-wingers. So why do I keep on finding surveys proving mathematically that people who support Bush are less likely to be well-informed about concrete, provable, relevant facts than people who support Kerry?