As Valve announced back in August, they are currently working on a Steam client version for Linux, Ubuntu to be precise. And this Linux client of Steam seems to be coming in a beta form somewhere in October this year, according to various sources.
The very first beta will include Left 4 Dead 2 and a couple of other titles, still to be announced.
The most interesting part of the Steam Client release on Linux will be that Valve has done a lot to optimize performance of the Source engine:
“Left 4 Dead 2 is running at 315 FPS on Linux. That the Linux version runs faster than the Windows version (270.6) seems a little counter-intuitive, given the greater amount of time we have spent on the Windows version. However, it does speak to the underlying efficiency of the kernel and OpenGL. Interestingly, in the process of working with hardware vendors we also sped up the OpenGL implementation on Windows. Left 4 Dead 2 is now running at 303.4 FPS with that configuration.”
As soon as we have more information we will ofcourse post it here on GameConnect.net