As a non-member, I agree with the policy not to watch movies that have gratuitous violence or sexual content in them, even as an adult. However, I wonder if it is overly simplistic simply to say "Don't watch R-Rated movies". If the Church had its own ratings board, then I could see that being a viable thing, but in effect it is saying to rely on the judgment of the MPAA as to what you should or shouldn't watch. Firstly the MPAA categories are overly broad, and secondly they're very inconsistent, as has been noted earlier.
Not only are movies such as Schindler's List lumped in with all the frat movies, I also find that some MPAA ratings seem to be biased in favor of or against a certain message, e.g. I did not find anything in the movie Kingdom of Heaven (with Orlando Bloom) to warrant an R rating, and I can't help but feel that the MPAA was unhappy with the movie's negative portrayal of the Crusaders.
My wife and I have resorted to all but ignoring the MPAA ratings wherever there is a Netflix rating available. Netflix has a very detailed rating system that not only looks at age-appropriateness, but also at specific examples of immoral behavior, language, drug- and alcohol use, etc. This was brought home to us recently as we watched the new movie "Fame", which was rated PG but should have at least been rated PG-13 due to a lot of objectionable scenes, in my view. When we later looked at Netflix, they had rated it "Iffy for 12+" and listed all of the things which I had a problem with. Had we first looked there, we would not have watched it with our kids. An opposite example is the movie "Frost/Nixon", which the MPAA rates R but Netflix says is OK for 14+.
I think ultimately we cannot rely on someone else making the decision for us. We need to educate ourselves and use our own best judgment to decide what is healthy for our kids and ourselves to watch. This may include making trade-offs, such as allowing kids to see a movie with a few bad words (which they hear in school every day) but which otherwise is a good movie with an important message.
Just my 2 cents...