Making blocks with a MakerBot is almost counter productive.  Why would you want to make something out of plastic that can be used to make other things out of plastic?  Why not just print the final plastic object as a single piece all at once?

I like the idea of being able to physically play with the design of something.  Sketchup is easy to use, but legos are even easier.  I never worry about an operation that I can’t Ctrl-Z my way out of.  Plus, it’s even easier to go from idea to objection with physical building blocks.  I think it would also be a very interesting way to get around the overhang and size limitations of a CupCake CNC.