I've walked away from signup at sites where I'm mildly curious, and when I go to sign up - I have a 25 char random password-safe generated string rejected as a secure password due to stupidly enforced lowest-common-denominator rules. (Or worse still, rejected as "too long").

If Im feeling "community minded" that day, I might email their contact address and tell them why I didn't complete the signup process - if I'm in a stabby mood I'll more likely just lampoon them as morons on Twitter. doubt either action on my part makes any difference.