The best example I can think of is the Bible. At my high school they started a course called "The Bible as Literature," and it created quite the controversy. Before it was all over (and, in a way, it still isn't) there was a team of ACLU lawyers preparing to take the school district to court saying they violated the separation of church and state, and people were driving around with bumper stickers that read "We Support the ECISD Bible Curriculum." The base of the schism was that many Christians in town felt as if the bible wasn't "Literature" at all, they felt it was a book to live by.
This episode is what originally made me decide that literature is relative. What I consider to be of literary merit might read like complete poppycock to someone else, and visa versa. Two of my favorite authors are Shel Silverstein and Theodor Geisel (Dr. Seuss). Occasionally I'll get into an argument with someone about how important Silverstein and Geisel's works are in the grand scheme of all things literature, but people usually agree or at least see my point of view on the subject, which tells me that people are generally willing to accept that their schema of literature might differ from other people's, and that it is okay.
It might seem like a cop out answer, and maybe it is, but I can't help but think that literature isn't something that should have a set of requirements. It seems to me that as long as you walk away having learned something substantial from whatever you read, and enjoyed yourself in the process, it was literature.