I recently tried to reconfigure my Time Machine with my AirDisk on both my MacBook Pro and MacBook to a new drive I setup on my AEBS. The drive is formatted HFS+, the sharing permissions are fine... and Time Machine does not allow me to use the volume for Time Machine backup. So I decided to plug the old drive in that had my old TM archives on it, and now TM won't see that one either. If I select "Browse Other Time Machine Disks" from the Time Machine icon's context menu, I *am* able to see my old Time Machine archive (and browse) it from my AirDisk, but Time Machine will no longer let me backup to it. So I decided to go to the Apple Support site, and found an article that was added less than two weeks ago: http://support.apple.com/kb/HT2038 Time Machine in Mac OS X 10.5 Leopard can be used to back up to many kinds of Mac OS Extended-formatted drives, but it does not support AirPort Extreme's AirPort Disk feature.