I'm saving up to upgrade my PC (AMD HSA on Kaveri + DDR4) because of SteamOS (amongst other things) instead of getting a next-gen console. And I know a few other people doing that as well.
AMD needs to move to 14/16nm FinFET in 2015 as soon as possible (like Nvidia is doing). Everything is great on the GPU side, especially with all the added parallelism features, but they really need to close up that gap as much as possible with Intel on the CPU side. They can't do that by being 2 process nodes behind Intel, no matter how much they will innovate on the CPU side in the next few years, too.
If they try to be on the most cutting edge process node as early as possible (that's available to them), that could make them quite competitive and appealing, especially as all-in-one solution for gamers. I'd certainly consider them myself, too, but not until 2015, and until they jump to 14/16nm FinFET.
I am doing the same, once the OS gets released and I can buy controllers I will be hooking it up as the main system. The thing steam gets right is that everyone in the house who uses games has a great experience, from 10 - 35 years old it is extremely friendly and useful.
I have been using Steam on Linux and once they get a few more titles final (like CS: GO, they already have DOTA) it removes any need for Windows (home life isn't very Office centric).
I've also been doing this. I have a pretty beefy windows machine that I have configured to launch into big picture mode on boot with an Xbox 360 controller and the experience is about 85% there. It is kind of a pain in the ass having a controller, a keyboard, and a trackball in my living room in addition to the TV remote stuff.
It's also annoying to have a full desktop PC in the living room. When game streaming lands in Steam I'll be able to move that entire box into my office and then just have a simple front end Steam Machine handling driving the TV. People keep posting pics of the streaming UI but they haven't turned it on yet.
For my "front end" machines I am using 2 Ubuntu laptops with background auto updating turned on, steam in big picture mode on boot, and either an Xbox controller or a Logitech 710. I am thinking those will hold me over until Valve starts publishing the case CAD files and I'll be able to build my own proper machine.
