I am curious about the enclosure they've built to minimize heat and noise coming from the GPU and the 450W PSU.

A couple of years ago I built a small AMD Llano based computer using a small enclosure sold by Mini-Box and an 80W fanless Pico Power Supply also sold on the site.

Case - http://www.mini-box.com/M350-universal-mini-itx-enclosure

PSU - http://www.mini-box.com/picoPSU-80

It is much quieter than an Xbox 360, but also can't play any XBox level games on it (I use it as an HTPC). I'd be curious to see what I can do today with the same amount of power using Haswell, some 28nm GPU and SteamOS.