Valve will soon be implementing a great new feature within Left 4 Dead that, courtesy of Steam's obsession with cataloguing data, will be able to track and display your game stats.
This new stats page will be able to track you performance (kills, deaths, survival time, etc) over time, and show stuff like how often you use each weapon and play as each character. It will then allow you to compare your stats to other players, letting you swing dicks with your friends as well as seek out other players of a similar skill level to your own.
You can even filter out "undesirable" types, as the stats will also record things like how many times a player has killed their teammates.
The more general statistics have been tracked within the game since December 12, 2008, while weapon-based stats have been gathered since February 11.
The stats page should go live any day now. While you wait, you can check out the level of detail Valve have gone to in the screens below.