As for the question on energy consumption, the original Xbox 360 had a power brick rated to 203 watts, and it got hot. Nearly two years ago I got two 360 S consoles and their power bricks are rated at 135 watts. The newer E console has a 120 watt PSU.
The 360 S 4GB console is the only thing plugged into the bedroom TV. With the exception of the occasional game, its on about 2 to 3 hours a night as Media Center Extender, or for Netflix, Hulu+, or Amazon. After all that use, it is still extremely quiet, and my wife is still happy with the setup. If you care at all about noise, the S or E console is the way to go.