My experience with wingnuts was limited to that Montgomery Wards bike, and I don't recall any issues with them... but I wasn't putting a ton of miles on it. I wonder if any of our C&V friends have extensive experience?

Considering the general popularity of wingnuts for high end bikes for some time(?), I'm guessing that slippage wasn't a serious problem. If it was, it wouldn't have been that hard to just go back to nuts and a wrench. Tullio Campagnolo is said to have invented the quick release because he couldn't loosen a wingnut. No mentions of any slippage issues. If I had to guess, it might be the case that you had to really lean on those wingnuts to avoid slippage, thus making them hard to remove when dealing with cold temperatures??

Looking at Tullio's timeline again, I see that he came up with the idea in 1930. I think wingnuts continued to be used for some time after that, but don't currently have any data to support that hypothesis. I still find them interesting.

Steve in Peoria