Use the stats page to track your performance; see which aspects of your gameplay are improving over time, which are your go-to weapons, and how often you use various characters and features.
You can also use your stats page to compare your statistics against other players, giving you a quick and easy way to see how your accomplishments measure up to your friends and find players at your own skill level. You can also track negative statistics (like damage dealt to other teammates, for example), giving you a good idea of which players to avoid.
The stats page is broken up into four different pages: Overview, Weapons, Versus and Survival.
You can find your own stats by going through the Steam Community, and can read about the stat additions on the Left 4 Dead blog.
On top of this, there is a sale for Left 4 Dead on in the Steam store, saving you 40%, and a free 24hr trial of Left 4 Dead for today only. So now there's no excuse not to face the zombie hordes with your mates.
