Andy Carol is a Lego builder who created a working Difference Engine in legos, though his machine "only" solves second- and third-order polynomials to three or four digits. The site contains fascinating detail about the workings of Difference Engines and Carol's implementation thereof. Link (Thanks, Rick!)
Update: Paul sez, "The original work by Babbage wasn't
funded by Ada Lovelace, it was funded by the British government. The
original difference engine did work, and quite well - it was able to
provide thousands of corrections to naval tables of the period. While
still developing the difference engine, however, Babbage began to
expand his idea - into the *programmable* analytical engine. This is
the machine for which Ada developed a programming language, however
the work was still funded substantially by the government. Political
issues, not technical limitations, are what ultimately killed the
project. Babbage had no social skills whatsoever, many in the
government hated him. "
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.