Steam Linux beta coming next week27 Sep 2012
The beta will include testing for the functionality of Steam on Linux, one Valve game and support for Ubuntu 12.04 and beyond. Third-party games, Steam Workshop etc will not be included.
Valve has yet to officially confirm which game would be included in the beta, but Left 4 Dead 2 has been mentioned previously.
The word from Valve is that the beta will be a good chance for Linux users to ogle at how well Steam is looking on the operating system. However, the recommendation for newcomers to Linux is to wait for the full Steam Linux release, which will pack more features and be easier to install.