If you bought Left 4 Dead 2 at launch you more than likely experienced the craptacular lagfest that has been Left 4 Dead 2 multiplayer. Late yesterday Valve put out this statement, "We have upgraded our network infastructure to better accomodate the huge response to L4D2. 360 Players will now have lag-free servers. We've also added more dedicated servers.
We will continue to monitor the situation and add resources as needed.
Thank you for your patience. Now quit reading this, get out there and kill some zombies!"
While many games cannot recover from an utter fail at lauch like Valves Left 4 Dead 2, its almost a certainty the online community is gonna forgive and forget.