Apple released AirPort Extreme Update 2008-003, but then pulled it several minutes later. The update now no longer shows up in Software Update, and the page it was on is missing from Apple's site.
The update was originally recommended for all Intel-based Macs with Mac OS X 10.5.5. The update said it resolved "some issues with AirPort connections when roaming in large Wi-Fi networks."
The file was available from this page on Apple's website, and via Software Update. It's unclear why the update was pulled, or if there are any consequences for those who have installed it already.
If you installed the update, do you notice anything amiss? Let us know by leaving a comment.
Thanks, Danny and Randall!