The concept of Steam OS is interesting, but Valve getting into selling hardware (Steam Box, not the controller) may be a mistake. One of the benefits of PC gaming is the ability to customize your own system to fit the needs of the games you play, at your own budget. Steam Box seems to be just a linux PC sold at a premium price due to branding and form factor. The hardware side just doesn't sound so appealing especially when many current PC gamers already have a system that can run their games, and are just an upgrade or two away to play future releases.
I can understand the appeal of playing in your living room on the big screen, and not having to lug your existing tower to play there. However, even if you were in the market for a living room PC, you can purchase similar or better parts individually at the same or lower price point (we'll get a better picture when pricing info is released, but generally making your own system is cheaper), and install Steam OS yourself or play in big picture mode.
I would be interested in buying the Steam controller though, depending on the price-point and reviews. Even if the design is new, the functionality is the same as any other controller, so if it is too expensive, I would just stay with the well-made, inexpensive and comfortably familiar Xbox controller.
