That's cool. I wonder how hot the coffee has to be to get it to work (you can really tell where my priorities are).

Make Magazine had an article last year (issue #7) on building your own Stirling engine using, among other things, empty tin cans for the pistons and cylinders. It was very cool looking, but I haven't gotten around to it yet. I'd like to do a hack of this project combined with a solar concentrator to provide the external heat source.