I was surprised to see that this movie was recommended for kids 13 and older, and when we watched it as a family, I was even more surprised! I thought that the main topic of concern - sexual themes/content - was generally appropriate for my kids, who were 9 & 10 at the time. "Marital relations" in the movie were just that - the relationship between the main couple, who are married, and choose to have a family. With kids going through puberty at the end of elementary school and the beginning of middle school, I feel like healthy, positive presentations of adult behavior are sorely lacking. I'll take this over violence/drugs/language any day. (Case in point: Child's Play gets an age rating of 12, with 4 stars for violence and 4 for language.)
It is true that the friend of the main character does use the dog and later the children as ploys for meeting women, and while disingenuous, this never turns into a relationship on screen and really is just a comic diversion.
I also did not find the references to marijuana and alcohol problematic, although I could see that being a more legitimate concern.
All in all, particularly with the way the movie sensitively deals with the end of Marley's life, I felt like Marley and Me was well done and family friendly, and certainly more so than many movies with violent content.