Kubuntu 9.10
I've been using Kubuntu 9.10 for a little over two weeks, and despite a few annoyances, it's been great. Sound and WiFi worked out of the box. My biggest gripes have been with Kopete and Amarok. I ended up replacing Amarok with an older version of itself, and Kopete with Pidgin. Also, Firefox seems sluggish when I have a lot of tabs open, and sometimes tabs lose their ability to be click-dragged and I have to restart the process. But the only time I've ever been forced to restart the system is when I accidentally made a shell script call itself recursively. (I'm sure there's a way out of that. Now that I think about it, I probably should have tried killing the parent process.) So far I haven't had to build anything from source to get things working how I want. They even added Kyoichiro Suda's focus blur plugin to the GIMP plugin registry. And I love how my desktop looks!