I wrote a review of Keith Olbermann's Countdown show some time ago. Basically, I wrote that his show is good so long as you only watch it in small, bite-sized Youtube clips. Other than that, he's pretty much a partisan hack, and even though O'Reilly might deserve it, Olbermann nitpicks away at him (and other conservatives) a bit too much.
With that said though, he really hit the nail on the head when it comes to Prop 8. Anybody who voted yes on it should have to watch this.