In 2008, Valve quietly posted a job advertisement for a software development position with the goal of simply "porting software" to the Linux platform in several of the trades. Valve confirmed this was in fact really them, and although they were mum on a number of details, and received only minor attention from the gaming press, this seemed to be the beginning of Valve's embracing of everyone's favorite open source operating system.
In the interim, Gabe has "bet everything on open", and when he said open, he meant open platforms. At the time he spurned XBox Live as the primary target at his dissatisfaction, but he went on to mention closed systems like those Apple creates are destructive for overall industry health. Then Valve reversed course on their anti-PS3 position, praising Sony for adopting a more open and developer friendly approach.
And then of course, Valve ported Steam and their Source engine to the Mac in 2010. Half Life 2 all the way up to Portal 2 is now available on PC, Mac, XBox 360 and the PS3. At the time, they said they would next be porting everything over to Linux. Time frame? "Eventually." Valve, being notoriously slow to develop titles, didn't inspire a great deal of enthusiasm in the Linux community with that response.
Now, in 2012, Valve has started a new blog, dedicated to their Linux developments.
To summarize their current status update, they're finalizing the Steam client to be fully functional on an Ubuntu platform. Their 2009 title Left for Dead 2 has been completely ported, all though they are working on extracting the same speed the Source engine is known for on the Windows platform. The likely culprit is drivers.
It's an interesting development from a team born out of ex-Microsoft employees. While it's great to see a company "betting everything" on open platforms such as Linux, this could also be interpreted as a lack of faith in Microsoft's future in the Operating Systems market. With much uncertainty about Microsoft's wackier decisions for Windows 8, perhaps it's closer to the mark to say Valve is hedging their bets? I wonder who will "jump ship" next and embrace open.