Lulzboters,
On a recent print we ran into the issue of the extruder head mounting bracket disconnecting itself from the overall larger extruder assembly. The object we were printing had some thin sections that required the extruder head to move back and forth very rapidly. Over time this giggling caused the two screws that hold the aluminum extruder mounting plate to unscrew because they are mounted upside-down. This created a pretty amazing fluffball of extruded plastic!
To fix this, we just used 2 lock washers on these screws and have not had any problems since. If you are running into issues with the components in the extruder unscrewing on parts that include a lot of fast direction changes, this might be something to try.
Also, might be something to include in the next version of the printer 