[dnanian]

Being able to attach an HFS+ volume to the Pogoplug (which you can do with the Airport Extreme/Time Capsule, too) doesn't mean you can actually write directly to it with SD (in fact, over a network, you can't). The file system is abstracted by the networking layer (netatalk, most likely).

However, it does mean you can use the trick described in the "Airport Disks" post at the Shirt Pocket blog to speed up your first backup and subsequent smart updates.