http://forums.steampowered.com/forum...d.php?t=535896
18. Release dates. Well as of this moment, it's said to be Q2 2007. I've heard Summer and Spring. We just don't know yet. But what I do know is that it's coming soon so be prepared!"
18- They talked about Spring-Summer, i bet on April-May.
Left 4 Dead-specific update will be made to the Source SDK so members of the community can make their own missions,
Are there any noticeable signs of injury? - When a player gets low on health his/her movement slows down.
How long will maps last, and how many campaigns? - Large maps are said to last upwards of 40 minutes to an hour. Four campaigns at release with five maps per campaign (for a total of 20 maps at release).