Well in my case, I'm going to have to go wireless anyways (due to the lack of ethernet on the ground floor, and difficulty of changing that), and I've got a perfectly good little Linksys USB 2.0 wifi thing sitting here. However, the USB ports on the Xbox are only 1.1, so I'd have to buy a wireless<->ethernet bridge as well...

Short version: I can do a vast collection of hacky crap to the Xbox to make it vaguely resemble a decent system that can do wireless, and have a non-sucky DVD drive, *or* I can just build the Mini-itx system and have a lot less stress (plus a quieter system for movies, which is more important than for games, which are in general quite noisy).