In yesterday's PDN, Media Matters' Paul Waldmann has a column about the lack of actual liberals on cable news and CNN's hiring of Glenn Beck. I do disagree with his characterization of Olbermann as a "progressive" as whatever his strengths Olbermann doesn't really have an ideological show and he's not out there advocating for a progressive policy agenda. Olbermann, like Dan Froomkin and Jon Stewart, recognize that it's basically their job to call bullshit on the people in power whoever they happen to be. I imagine he's probably more liberal in his politics than, say, Tucker Carlson but it rarely comes through on his show.
During the Lewinsky nonsense Olbermann was the only cable news host who understand the power dynamic, until he quit. While Clinton was president and certainly had a lot of power, the real "power" on the Lewinsky issue was the Republican Congress, the conservative media/movement, Starr's OIC, and the Washington press generally. So, Olbermann, when he could, called bullshit on that.