Great product line extension from Apple today -- AirPort Express. There's been a literal missing link in the Apple line between iTunes and the home stereo, a link that's been filled in the market by products like the Slim Devices Squeezebox. AirPort Express / AirTunes is critical for Apple for two reasons.
First, it keeps the iTunes UI front and center for music selection and playback in the home. Other products (like the Squeezebox or the Tivo Series 2) put their UI in front of the user and relegate iTunes to ripping and management. Apple needs to control that every day user experience if they're going to drive incremental "casual" business to the iTunes Music Store.
Second, it makes it easier for home users to get FairPlay protected AAC files bought from the Music Store across the house to the stereo. I'm not sure about Tivo, but Slim's device can't play songs purchased from the Music Store, since Apple hasn't licensed FairPlay for use on other devices. Users have had to resort to third party utilities like PlayFair, or an inconvenient round trip buy-burn-rip dance in order to get their music across the house. With aggressive marketing, Apple's product just might nip the external device market in the bud.
Update: ordered one. Ship date is mid-July.