Modern Warfare 2 at Gamestop right now may not know about it, but Activision says a recent survey concluded that 82% of gamer parents are well aware of the ESRB rating guidelines and what they mean. The survey also found that 75% of children who play games understand the rating system, and that 70% of parents actually pay close attention to the ratings when buying a game either for themselves or for their families. Note that it doesn't say they follow the ratings, only that they are aware of the system and pay attention to how games are rated.
Gaming families spend a lot of time playing games, too: 76% of parents agree that video games are a big part of their family activities, and among gamer parents, a majority (52%) of their gaming time is spent playing with their children. Finally, a full 59% of kids polled say that "it's a little creepy" when Jane Lynch shows up to play games with you for a Microsoft commercial. Okay, you got us, we lied about that last stat. When anyone from Glee shows up, it's 100% fun.