According to a Washington Post story by Howard Kurtz, about 200 advertisers have "joined a boycott" of Glenn Beck's program, with Apple abandoning Fox News altogether. From the story:
More than 200 companies have joined a boycott of Beck's program, making it difficult for Fox to sell ads. The time has instead been sold to smaller firms offering such products as Kaopectate, Carbonite, 1-800-PetMeds and Goldline International. A handful of advertisers, such as Apple, have abandoned Fox altogether. Network executives say they believe they could charge higher rates if the host were more widely acceptable to advertisers...
... By calling President Obama a racist and branding progressivism a "cancer," Beck has achieved a lightning-rod status that is unusual even for the network owned by Rupert Murdoch. And that, in turn, has complicated the channel's efforts to neutralize White House criticism that Fox is not really a news organization. Beck has become a constant topic of conversation among Fox journalists, some of whom say they believe he uses distorted or inflammatory rhetoric that undermines their credibility.
Fox News has become the "American Idol" of cable news, utterly dominant, so much so they're planning to target mainstream entertainment networks such as USA and TNT at their upfront pitch to advertisers. But its easy to forget that ratings only matter if your numbers can successfully convince advertisers to purchase time on a program. To hear Kurtz tell it, Beck's program is like that "Twilight Zone" episode where a librarian is left alone with a million books and a broken pair of glasses.