Just so people know, Valve implements their L4D "matchmaking"(I use the term loosely) using dedicated servers.
http://www.1up.com/do/newsStory?cId=3169669
"After spending a day at Valve's offices playing Left 4 Dead for the premier episode of the next season of the 1UP Show, the 1UP crew came away with a truckload of new info on the Xbox 360 version of the game. Without a doubt the biggest news is that Valve will be running dedicated servers on Microsoft's Live online service. And while they didn't indicate how many exactly they'd have going, they did imply that they'd have everyone covered, as in when you played online, you'd be on a dedicated server, period. That alone should go a long way toward making the game a great online experience, but they haven't stopped there. Splitscreen play will also allow you and a friend to play together on Live from one 360, and you'll be able to slice the screen whichever way you like -- horizontally or vertically."
This is in response to the person above griping about L4D not having dedicated servers.
