The Left 4 Dead 2 web-site has been updated to further reflect last weeks' Valve Linux news
: Left 4 Dead 2 will be natively released for Linux this calendar year.
The Left 4 Dead 2 Cold Stream
now says, "Later this year, L4D2 will be available on a brand new platform. It will be one of the first Valve games to be released on Linux. This will allow Linux users to run Steam and play the game directly without having to run additional software. You can follow the development HERE and we will have more information later this year as we get closer to release."
There's also a photo of zombie-ified Tux: