I dug down into the folder you're talking about bmike. The most interesting folder appeared to be OneNoteOfflineCache_Files, but when I tapped on each of the .onebin files, they appear to be just graphics files representing menus and such that you see when you're in OneNote.
The only other folder with something in it was ServerListings and that has a single .onesrvcache file that doesn't look like it has data in it either.
then I took a look at OneNoteOfflineCache.onecache using TextWrangler. It's full of unreadable glop but then I found a section in actual English talking about taxonomy of polar bears! Emboldened I did a search for a term I'd used in a notebook and sure enough my data was in there. Oddly not everything I wrote in my note was searchable, just some terms.
Fun stuff - not terribly useful if you're thinking you can get to that data without OneNote, but still fun in a geeky kind of way. I did find a $20 (Normally $40) application called Outline that says it will open OneNote files though: https://itunes.apple.com/us/app/outline/id604802021?mt=12