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Update: Version 1.0.0 is out of beta and this topic is closed. Please post questions/suggestions/bugs in the other threads.
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Here we go..
I've been working on this for a while, and thought you might like it:

It runs in the background and detects your iPad/iPhone/iPod touch on the network when it's running ShutterSnitch. It then backs up any new changes to a folder on your Mac.
..yes, only for Mac OS X (10.6/10.7) at the moment sorry. Time is not on my side, but I'm very interested in seeing this on the Windows platform too. If you're a Windows developer and would like to help with this, please leave me a note!
Edit: beta download link removed.
The app will eventually be a free download on the Mac App Store.
Please feel free to leave bug reports and comments here!