Valve's Robin Walker (aka Bro, who you can see here
after he roundly thrashed yours truly in a Quake duel at Armageddon 3 back at the dawn of time) has posted to the Team Fortress 2 blog
detailing a new strategy to try and help improve the player experience when it comes to finding good servers to play on:
In short, servers that have lots of players joining & leaving rapidly will score badly. Servers that consistently have players join and stay on for long periods of time will score well.
Our first step in improving this part of the player experience has been to delist all the really bad servers. The master server will simply stop giving these to you when you fire up the serverbrowser. After that, we're going to keep improving our ability to measure this kind of problem.
Not sure if I am a huge fan of this scenario - I've always liked the complete democracy of servers available in games like this, and I'd be concerned about how people could abuse the system (eg, if I wanted to de-list someone's server, could my douchebag friends and I just join it and leave it over and over?). At the very least it'll be an interesting experiment. Stay tuned!