I first joined Daily Kos in 2004, during the darkest days of complete Republican control of the federal government. What's kept me here so long? There's a value to this place--one that we've appreciated for a long time, and one that is only now being appreciated in the outside world.
Back in my sophomore year at Carolina, I attended a lecture by Gene Roberts, the former executive editor of the Philadelphia Inquirer. He lamented how cutbacks to our newspapers have limited their ability to cover politics the way it was supposed to be covered--incrementally. He was pretty blunt about it--"If you don't cover it incrementally, you don't cover it at all." Daily Kos fills that needed role. Arguably, the best example of this is this site's coverage of Scott Walker's wingnuttery in Wisconsin. As much as it has been covered nationally, the posts by the Wisconsin Kossacks have given us a front-row seat to the efforts to call out the fail.
Daily Kos also allows us to bring needed sunshine to issues that would otherwise go unnoticed. For instance, I doubt that most people would have even known that Westboro Baptist Church was actually planning to Newtown and picket the funerals of five- and six-year-old kids if not for Daily Kos. I must say that I'm not completely unbiased on this, as I've spent a lot of my days scanning news sites and conservative sites for things that the community should know about. After all, somebody has to keep an eye on them.