Ars Technica reports that Apple has removed all mention of wireless backup support from their page on Time Machine. It used to read:
Effortless meets wireless.
With a hard disk connected to your AirPort Extreme Base Station, all the Macs in your house can use Time Machine to back up wirelessly. Simply select your AirPort Disk as the backup disk for each computer and the whole family can enjoy the benefits of Time Machine.
This is a shame. This is one of the things about 10.5 that I was thinking was going to be very neat. If you have a desktop computer, it’s easy to plug in an external drive for backups, but with a laptop, not as much. You have to plug it into the drive every once and a while and leave it awake so that it can run the backup, which eliminates the entire “set it and forget it” convenience that Time Machine was supposed to deliver. Reportedly wireless syncing was working in earlier builds, so it’s likely that Apple yanked the feature because it wasn’t working reliably. Posters on the Apple support boards think that a firmware update to the AirPort Extreme base stations will be able to make it work again. Until then I guess I’ll put off buying a backup drive.
Update
Walt Mossberg’s Wall Street Journal review states: While Time Machine can perform backups over a network, the backup destination can only be a hard disk connected to a Mac running Leopard. So if I plug a drive into my iMac, a MacBook on my wireless network can backup to it, but not if the drive is plugged right into the router? Or maybe I’m reading it wrong.
Update 2
So here’s the deal, apparently: AirDisk syncing doesn’t work. Apple made a few file system changes under 10.5 for Time Machine, so it’s possible that an update to the AirPort Extreme stations will fix this, but for now, you can’t do it. You can, however, plug an external drive into one of your computers, set it to share over your network in System Preferences, and then tell other machines to use that drive for Time Machine. Performance is probably slow, but once your initial backup finishes it won’t be syncing a whole lot of data with the periodic backups.