... I hardly ever use unless. I never use negated expressions or expressions with more than one term with unless ...

That tends to be my practice. I will quite often use a statement like
    next LOOP unlessX;
for loop control where X is a fairly simple condition expression; otherwise, I agree that unless (and his scruffy pal until) are just too mind-bendy. (I think I remember TheDamian recommending this practice in his PBP.)