It's an official group for the beta which is hopefully coming soon that appeared on Wednesday. There are no news about the beta and there has been no clarification about this page's purpose. Nothing has been announced yet.

Looks like it's gonna be a closed beta.

They did say, in a post entitled "External Beta News" [1], that a private - but again, external - beta is to be expected in October.

[1] http://blogs.valvesoftware.com/linux/beta-late-than-never-3/

Hopefully you get access by joining to group.