Valve's Linux team has started a blog detailing what, exactly, it's up to. The first order of business was to port Left 4 Dead 2 over to Ubuntu. Currently, they are "getting the Steam client onto Linux with full functionality," "optimizing a version of L4D2 running at a high frame rate with OpenGL," and "porting additional Valve titles."
"Our mission is to strengthen the gaming scene on Linux, both for players and developers," reads the blog. "This includes Linux ports of Steam and Valve games, as well as partner games. We are also investigating open source initiatives that could benefit the community and game developers."
While I don't run Linux myself, I feel as if this and the Humble Indie Bundles are a big step in the right direction and ought to lead to cool opportunities in the future.
Steam’d Penguins [Valve Linux]