Apple has released an update to AirPort to version 3.3.1. The new version is intended for AirPort Extreme and AirPort users who are on AirPort Extreme networks. The short description from Software Update Control Panel:
The AirPort 3.3.1 Update improves the reliability of AirPort connections when changing network locations. The update is recommended for all users with an AirPort Extreme and AirPort enabled computer or an AirPort Extreme base station.
You can find the update in the Software Update Control Panel. The update weighs in at 812 KB. A restart is required after the update. You can find more information on AirPort at Appleis Web site.