Thanks - then are you aware of any AirPlay compatible stereo systems?
I'm not entirely sure if anything has actually been made available yet. As in, you can buy one. Any sufficiently complex receivers should in theory be upgradable (firmware update) if the manufacturer wants the AirPlay feather in their cap.
Denon has the AVR-4311CI. MSRP is ~$2000. AirPlay is being added as a firmware upgrade.
Marantz has the Melody Music (M-CR503) receiver, which will be ~$700 MSRP.
B&W, JBL and iHome are listed partners. Obviously, AppleTV is an inexpensive option. My guess is it'll be something more prevalent in the next annual refresh cycles for manufacturers. Some such as Denon are being aggressive with firmware instead, and will presumably introduce new models with it standard. Pluuuus, you're still waiting for application developers to take advantage of the new protocol.
I'm waiting for digital sound projector (soundbar) manufacturers such as Yamaha to start including support. AirPlay would be a "nice to have" when I do finally do the "home theater" (wall-mount the current TV, DSP, and a long, shallow bench to visually anchor everything with).
TL;DR It's coming, slowly. It'll pick up steam in 3 to 9 months.