The Linux team at Valve is looking for beta testers for the Linux version of Steam. A comment about it was discovered on the Valve's Linux Blog, according to which everyone wishing to participate in the beta program should express interest in a comment on the Valve's Linux Blog or in an e-mail written to email@example.com. Here is the text of the Valve's comment:
At this time, we are collecting interested persons for possible inclusion in an external beta in the future. If you have expressed interest in a comment or email, you’re on that list; nothing more is needed.
It looks like the beta testing of Steam for Linux will start very soon. Just recently, a new entry for "Steam Linux Beta" has been discovered in the Steam database. So it 's simply a must to apply for the beta participation!