My favourite comment regarding Duff's Device is from Tom Duff himself:

"Many people have said that the worst feature of C is that switches don't break automatically before each case label. This code forms some sort of argument in that debate, but I'm not sure whether it's for or against."

My favorite use of Duff's device is this optimization in TIS-100: https://reddit.com/r/tis100/comments/38hfvl/multiplier_optim...