I know we've done TCP over power lines before (hi, Pablo), but I heard recently that HP is doing ethernet through their power adapters. This might make Life With an Air more do-able. I work in an environment where wireless is frowned upon, and keeping an Air tethered to an ethernet port is kind of a pain in the ass.
I am sure, like Magsafe, there are patents obstructing other people from doing it. But a magsafe power/ether device would be awesome. Kinda would suck to trip over your ethernet cord and lose your connection, but then, it's a whole lot better than losing your motherboard.