Good news for me. I'm currently running Ubuntu 12.04 as my only operating system. I also have a huge library of Steam games that I'm currently not using as per the previous sentence. Running proprietary AMD drivers on my install and that will absolutely be a prerequisite for running any commercial game. L4D2 isn't my most favorite game but I do own it so it would be nice if I automatically received the Linux version. In future, with other Valve/Source titles it would be awesome if they were SteamPlay and I could purchase once and play on all supported platforms. And WINE? Yeah, it works a lot but then again it doesn't work a lot too. And sometimes you'll upgrade it and something that worked stops working too. So, native Linux versions would be much more desirable than leaning on WINE.