Cool find, Ken. I hadn't heard of MakerBot before, but have been following the similar Fab@Home for a couple of years now. It's looking like the DIY additive technology is on the edge of actually making useful parts.
Please do report if/when you build an extruder head. I think that's a fantastic idea, since the model-to-slices-to-gcode software is open source and freely available.
The closest I've come is adhesive/gasket dispensing using the old Isel gantry table. But this is a whole 'nuther level!