Did a little more surfing. Apparently, GM had them on some cars (Ponitac among others), through the 60's.

I guess there really was an issue with lug nuts loosening up. Don't know if the LH threads worked or not, but it was one attempt at a solution.

The 'fix' is the conical nuts that they use these days. The tapered part at the end of the nut must jam into the wheel so that the nut won't loosen.