As someone who isn't a PC gamer what is appealing about this to you so far? Basically at this point it is:
1) An OS you install on a HTPC to play some games natively and stream the rest from your current gaming PC
2) An OS you install onto a gaming worthy PC and give up anything released for Windows with the incentive that AAA support is coming.
3) An OS you dual-boot alongside Windows.
To put things into perspective there's under 200 native-Linux games on Steam with AAAs apparently coming next year. But obviously you won't see many (if any) devs porting their old games over unless this gets huge. That would also not apply to DirectX-powered games.
Honestly, unless they get some sort of crazy built-in WINE solution I don't think this is enough to appeal widely just yet. It's a start but once you actually sit down and imagine how you would use it you see that it's limited (or really expensive.) I definitely see this appealing to the crowd who have a computer in one room and don't want to run a 50 foot HDMI cord into another. I'm not in that crowd currently but I would have considered it in my previous apartment.
Like I said.. if this catches on. I don't like the Windows OS, I haven't used one I like since XP, and I'm not a fan of the direction Windows is heading as a platform. So if in the next few years, most PC games are being brought to the SteamOS, I'm open to the idea of having a computer solely running SteamOS, as gaming is all I'd ever end up doing on a PC since I have an iPad and a MacBook to due all my websurfing, music downloading, recording, video editing on. Or if nothing else, because it's free, I could install it on my MacBook, nothing to lose.
Still doesn't fix some of my major issues with PC gaming in general; compatibility issues with hardware, controller support, etc... but we'll see what Valve has to offer tomorrow.