In the past (and when I mean past I mean everything before Cataclysm) I would definitely see people who got reported be punished. But in the last few years I've seen repeat offenders get away scot free no matter how many times I, or anyone else, reprt them. Gold/account spammers especially.
So at the end of the day, Blizzard leaves me no choice but to just ignore them until my list is full.