As I mentioned in the Latest Acquisitions thread, I got one of these for Christmas, along with the extra tooling...
It's a simple tool; you clamp the special coated lead foil over the rubber mat, select a punch, screw it onto the handle, and press gently on a bare spot of foil until it clicks twice, and voila! A tiny nut is created. The operation takes about a half a second and is basically foolproof. The results don't rival the likes of those made by RB Motion, but are pretty competitive with PE products. Here is a example mounted on my model, it is roughly .5mm in diameter; you can easily flatten them out or leave them "dished" as they come off the punch:
Besides hex nuts, it makes square nuts, hex bolt heads (no holes) and rivet heads. I suggested they offer a range of punches to make washers and rings; they seemed receptive to the idea but didn't make any promises.
Not cheap, but a well made tool that I think will prove pretty versatile...