If there was some way to make this solution work it would also mean there is a way to make it safe to randomly unplug hard drives. Trust me, if Apple knew how to do that it would be done, and the OS would not chastise you for doing something stupid when you unplug your USB pendrive without telling it first. Since they haven't figured out how to let you safely unplug USB drives unannounced it seems like a bad idea to base a backup solution on what is in essence a wireless USB cable that is phasing in and out of existence.
I have not been able to get a Time Capsule backup to last much more than a month (even with 10.5.6) before becoming corrupt, even when backing up over Ethernet. So I think there must be other problems besides the disconnection ones that Gerbarg mentions. Time Machine seems to work well over FireWire and USB, however.
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