Holy crap, after all the rumours and speculation it's actually real!
I'm psyched. I don't know if anyone else is psyched, but I am. I've been a big Linux advocate for many, many years and the only thing I miss on the platform is gaming. It's why I do most of my gaming on consoles these days (haven't run Windows in ten years), though recently a lot of indie games have been supporting Linux (like the Humble Bundle stuff). But having a big name like Valve enter the fray is definitely a big deal.