Nice! I hope this leads to a number of nice benefits for the Linux platform such as improved OpenGL support and better performance. A surprisingly large number of Steam games work very well under Wine, but don't play as well or look quite as nice as they do when run under Windows.

Also hope to see this done in a way that means it can be ported to all distros and not tied to just Ubuntu, but I'm fairly optimistic about Valve doing the right thing.