Doc Searls asks of Apple's new announcement of an AirPort Express: "Why go wireless-to-wired?" It strikes me as a question from somebody who has had a very different experience using FM Transmitters than I have. I have an iTrip that allows one to transmit an iPod's output across the FM spectrum. It's not bad. But it is not good either. It's a constant game of cat and mouse to find a station to use. I've had significantly better luck, and quality from the wired solutions I've had. Further, this way it doesn't take a tuner. According to the documentation you can plug it into any powered speakers. So for that second room a set of decent computer speakers just became a nice way to listen to music.
Now for the feature I wish it had. I'd like to send different songs at the same time to different places. Send the pop music into the den where the kids are gathered while having the news on the kitchen speakers.