I bought an AirPort express today and have been toying with AirFoil. I can get my MacBook's DVD player to stream the audio but the lag is pretty bad after a while. At the time I was doing a few things though so that may account for it.
But I'm one step closer to a fully wireless house. :) I like that iTunes and AirFoil can stream to multiple wireless devices. In the new place I plan on getting surround sound speakers and an airport for every room, even the bathroom (though surround in there would be excessive) so the apartment will be absolutely saturated in sound. It'll be really easy to do. The hardest part, really, will be find speakers I like and in quantity enough to wire an apartment.
It sure will be fun though. :)