You can add as many tuners as you want to MCE now (with a registry hack, but works great), so there is no reason to have 2 boxes just for the tuner limitations. I created this setup back in the MCE 2004 days. My second MCE box is in the bedroom, and it would indeed be much better if I could get my hands on an Xbox360, since they make a great extender. I also used to share my movies among both machines, as well as the TV recordings, making it easy to finish watching something in bed.
The only concern I have about the Xbox360 is that it has a giant power supply, so I am not sure how the noise of that box is, or power consumption. If I had to do it all over again, I would probably have 1 main MCE machine (living room), and use extenders everywhere else (assuming the My Movies plugin works with it). Some companies are also coming out with MCE boxes which are the size of these extenders, which is another interesting option, but they are much more expensive than the extender solution.
