The Valve Linux blog states that they've been in internal and private external betas through the month with "one Valve game" which I assume to be Left4Dead2.
I think they'll be moving on to public release or beta soon, and maybe with more than just L4D2. TF2 had an update that implies moving for Linux support, and a Steam Community page for Linux just went up recently.
A while back the L4D blog mentioned getting Workshop support, and the post mentions Linux support:
(if you haven't been following, they've been using L4D2 as the testbed for putting Source onto Linux, so it's the Source game we're gonna see first out of the gate on Linux.)All of this will also be available not just on the PC and Mac, but also for Linux users as well starting in the middle of next month and rolling out from there. We will have more details as we get closer to launch.
And today, the L4D blog announced a free weekend:
So I might be wrong, but I'm kinda expecting this to happen this weekend, if not tomorrow.Starting this Thursday, the entire game will be free to play for the whole weekend. New players can begin pre-loading now
There's also a list on the Steam CDR parser for what applications are flagged for Linux support, not just "there's a Linux version available" but they're actually Linux-ready on the Steam end: http://marlamin.com/cdr/search.php?s=linux&searchby=os
Most of the Humble Indie Bundle games, Killing Floor is there too as they use the Unreal engine (I actually emailed them about that near the initial announcement, they said they'd look into it, GUESS THEY DID).
Another thing, Drew Bliss, Valve Software Engineer, will be speaking for 15 minutes at the Ubuntu Developer Summit in Copenhagen: http://summit.ubuntu.com/uds-r/meeting/ ... iss-valve/
This is pretty fucking cool.
update: Valve have released a survey for candidacy in the next beta: http://www.valvesoftware.com/linuxsurvey.php