Apple released AirPort Extreme Base Station (with 802.11n) Firmware update 7.2.1 on Wednesday. The update adds 802.11n Draft 2.0 certification.
"This update requires AirPort Utility 5.1 or later. If you have AirPort Utility 5.0 installed, you can update to AirPort Utility 5.2.1 by installing AirPort Base Station Update 2007-002," according to Apple.
The update also includes minor bug fixes.