It's not just the Intel team that's working a lot with Valve's Linux developers. I'm told just days ago that Rick Spencer, the Ubuntu Engineering Director at Canonical, paid a visit to the Valve headquarters to talk about Steam on Ubuntu. Other Canonical employees are also in communication with the Valve Linux team.
The focus of Canonical collaborating with Valve comes down to ensuring that Ubuntu will be an excellent platform for running the Steam client and the various Source Engine games to come. Sure, the games are closed-source and not free, but as Intel's Eric Anholt said this week at the GStreamer Conference: "It's exciting! Valve makes games people actually want to run, rather than most of the games we work with now... [Valve develops] popular games."
So while some may not be too fond of these companies working with the game studio filled with lots of ex-Microsoft employees, Canonical is just working diligently to ensure Ubuntu Linux is a great gaming platform and can fulfill Valve's needs.
As has been stated already, Ubuntu will be the first officially supported Linux distribution for their forthcoming Steam client release and Left 4 Dead 2 game. Valve's obviously targeting Ubuntu because of its size, but their Linux binaries won't be Ubuntu-specific and should also work with other Linux distributions.
There was no comment whether Rick had brought beer into the Valve Linux cabal.