As I often say, I am not a gamer... and therefore I hadn't heard of Valve. Now I know, though, and I am deeply grateful to them!
For those who, like me, aren't gamers: Valve is a company that develops games (including many that even I have heard of) and ways to distribute them (Steam). Valve recently confirmed that it's working on Steam for Linux, and we're starting to see some of the results, which will benefit us all.
Evidence? It's on the Valve Linux blog, in particular in the post "Faster Zombies". Left 4 Dead 2 now runs faster on Linux than it does on Windows.
OK, that by itself is meaningless to us on Second Life. It's how they did it that is important.
I am among those who are royally urinated off at nVidia for their lack of support for open source drivers. (It's bitten them in a sensitive place; a few days ago a security hole in their driver was made public. Had the driver been open source, how long ago would it have been fixed?) Unfortunately, nVidia doesn't care what I think... but it does care about a serious game company like Valve. (Such companies create the vast majority of the market for their hardware.) Because it cares, it's willing to work with Valve on issues with Linux drivers. (So is AMD, owner of ATI, and Intel.) That should mean better graphics performance for everybody. (Yes, even Windows users--while trying to figure out why the speed increase, Valve found an inefficiency in Direct3D that they can work around, or maybe Microsoft will do something about it... Whoa, I must be in a good mood to give Microsoft the benefit of the doubt.)
So, don't despair. To the extent that things not in Valve code improve, we will all benefit.
UPDATE: Second Life will be distributed on Valve's Steam network. (Thanks to Hamlet Au for posting with this news and more.)