Unfortunately, in the haste to get the MakerBots out the door for the holidays the guys at MakerBot left out opto-endstop kits on some shipments.  These guys have been super responsive even before I bought a kit from them, so I’m not that concerned.  Frankly, it’s a little bit of a relief that I can skip the soldering stuff for now and move on to some of the pulley making steps.

In any case, as I understand it, these are not vital to the proper functioning of the MakerBot and that they’re really just a failsafe if the ‘bot forgets the second law of robotics.