In a Gadget Lab article Sorrell covers this real problem for Stanza users.
Once the books are on there [Stanza], though, they’re stuck. You can jailbreak your iPhone and go fishing around in the file system, looking for the books. Or you can download a Java app that will churn through the iPhone backups on your computer and sift out the books within
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The full instructions are in the article and thanks to Charlie for a real boon to Stanza users.
