Apple has issued a new updated for the 802.11n AirPort Extreme Base Station.
The 4.6MB update,
AirPort Extreme Base Station with 802.11n Firmware 7.1.1, is described as including all the fixes shipped in the previously released version 7.1 software, and also introduces additional compatibility updates for the 802.11n network hub.
The update requires AirPort Utility 5.1. If you have AirPort Utility 5.0 installed, you can update to AirPort Utility 5.1 by installing AirPort Base Station Update 2007-001 for Mac.
Firmaware 7.1 offered a range of improvements for the support of Mac and of Windows clients, printing, file naming, keychain passwords and better support for USB network discs all appeared in the release.
The latest version of the firmware is available here.