I came across
www.kids-in-mind.com/ and it's fantastic! It's basically a review site based on a films content so parents can decide if it is suitable for their kids. Thorough descriptions of sex/nudity, violence/gore and profanity are provided. I admire it's intent, though I can't really see the point. Ho-hum... No the main reason for posting the link is how funny some of the descriptions can be. Just look up something like Pulp Fiction...
I bet they absolutely hate it when they see an obvious film like Hostel ready for rating! Though as I said, what's the point? If a parent is conscientious enough to seek out advice from a site like that, surely they are aware of a films vague intent? Just the cover is enough to know with a lot.