According to a recent study commissioned by the ESRB 90% of parents with kids who play games are aware of the ESRB ratings on the box. The study goes on to say that 85% of those parents regularly use the ratings when buying games. 60% of those parents "never" allow their kids to play Mature games, and 34% said they let their kids play them "sometimes". 73% of parents also check the ESRB rating "every time" before buying a game for their child.
Any reasonable person should know that Studies these days are pretty worthless. Anyone can buy a study and have it say whatever they want so I'm not surprised to see the ESRB order a study and have it go totally in their favor. Now this isn't to say that I wish these numbers weren't true, but I just can't believe it. Maybe I'm wrong not to believe, but I just can't get past the overwhelming amount of kids who show up on forums for mature games and confess that their parents got them the latest GTA, Halo, etc. Just go to the Gamefaq forums, where the majority of people are under 17, and see for yourself.
Also consider this: How many parents are going to openly admit to letting their kids play games they shouldn't? Even if it's anonymously via a survey I don't believe the amount of parents willing to admit to bad parenting (even if it's only to themselves), by letting their kids play adult games or ignoring the ratings, is going to be very high. Maybe I'm being too cynical, but in the "blame someone else" culture that we now live in it's hard to believe otherwise.
It would be great if parents raised their children properly and didn't allow them to play videogames that they shouldn't, but I live in the real world where parents have less and less time for their kids, shoveling them off to day care centers to be raised by strangers and strange kids. Parents are too busy doing a thousand things to worry about whether a game is appropriate, and would rather just shut their kid up by buying them whatever they want. Sadly, that's the world that we live in and the ESRB has to come up with more than just some study to make me believe otherwise.