I'd been thinking about getting a Arduino hooked up to the hifi and in the kitchen so that I could stream music across the network to various audio devices. It turns out Apple had the same idea some time ago and have the airwaves package, sadly limited to being through iTunes which I really don't like, but most of my thoughts of how it should work have been implemented.
However for fun, it still might be good to get something going, maybe even cheaper than the Apple hardware, hooked up to some cat5 cable and again getting power from the POE switch as well.