I've been stuck sick in my room for the past week and discovered quakelive. Wow. It's awesome to remember how much fun this game was. The in-browser features are actually quite cool. You can easily find friends, the match browser is very cool, and achievements are always fun (should have more...) The game itself is the same ol' quake 3. However there seems to have a wave of new players, which is cool for unskilled players like me.
And it works *flawless* in linux, with firefox.
And yes, having a god proportion of linux players there would look quite good for their future ports, I guess ;)