L4D Survivor Pack is available today (FREE) on XBox Live 360 and PC.  The pack is 101MB.   I have enclosed below the link to XBox.com's where you can set up a direct download to you 360.  I have also included a link (second link) to the official site that gives a detailed explanation of what the survival mode includes.

Go forth my friends and kill many Zombies.....Infected.....whatever!    

http://marketplace.xbox.com/en-US/games/media/66acd000-77fe-1000-9115-d80245410830/

http://www.l4d.com/blog/post.php?id=2417

Nice! It will give me another reason to play the game. ^^

Not out yet for PC...

Ill give it another go on my PC to see if its any good, i mean, its free. But i thought this game was way overrated!

yep, for PC it's out "later today" (Valve time, so be wary!)

anyway, it might be cool but what I really want is the SDK

I will be downloading this on Live as soon as I get home. No wonder my buddy just texted me asking to play L4D after work today...

Oh wait, this update has the SDK? Sweet! Looks like I might have to put off playing ExciteBots...

Cool, will download when I get home.

I've been playing too much Gears 2 (Horde Mode)

Just had a quick go and managed to survive just over 3 1/2 minutes on the new level.

Need to get back into this. VS mode on the two other campaigns should be great too!!

I have a feeling this is going to be a bitch in the later time levels. I am still at work, can anyone verify the difficulty, and do you get to select the level your time trial is on??