So I usually browse this forum for any news for L4D and I stumbled accross an appoximate relase date for the DLC!!!! So far all I have is April, which is way sooner than I thought!! That survival mode kicks ass, even though they took 15 out of the 16 origanial maps and revamped it to fit the mode. Although, they did create one whole new level called lighthouse. Looks pretty fricken sweet. AND its going to be hard!!! I read the article and vales developers and best players could only last 9 minutes, at their best time, so its not gonna be easy at all. Check out the link to the thread below for more details!
http://left4deadforums.com/17650-survival-pack-released-april.html