MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
When I got my I3, after a while I started noticing all kinds of extruder-related problems. It drove me nuts trying to fix it. Basically, as it shipped, the screws that held the gripping gear into place were just not set in right. I managed to take the spring off, fiddle around with the orientation of the gear, and then really tighten the set screws down, and haven't had a problem since.
I didn't quite have the same experience you did, but I did notice that when the gear was slipping a bit, it would not actually move the filament on retractions, so it would just grind a little on the filament during retractions, and then move forward, but kind of skip. I suspect on a print with more retractions it might have chewed it apart like you describe? Dunno.. Take the gear off and really tighten it up.
I flipped mine 180' so I could get to the screws easier actually.. That seemed to help.