Apple AirPort Extreme Firmware 5.5.1 for Mac OS X is Out

and available for download from this Apple web page. Here are the improvements that the new firmware brings:

• Hard reset behavior is improved. With this firmware version pressing and holding the reset button for more than 5 seconds will cause the LED to flash rapidly. This visual feedback lets you know you’ve held the button long enough to trigger a hard reset
  
• Resolves a potential problem with PPPoE configurations when updating from 5.4 or earlier
  
• Improved reliability of WDS networks when using WPA security. If you had a WDS network secured by WDS and then removed any of the WDS nodes, this could cause a memory leak resulting in the need to reboot your WDS network nodes
  
• Resolved an issue with inbound passive FTP to a port-mapped computer on the network
  
• Resolved an issue with certain printers which were no longer recognized by the base station after the 5.5 firmware update was installed. With the 5.5.1 firmware these printers are again recognized by the base station.

We installed the firmware update on our Extreme Base Stations with no problem. Fortunately, we didn't have any of the issues that the firmware update fixes. [Bill Fox]