A hell of a lot of horror movies are book adaptations or ’‘actual events”. I also read a lot of horror books so chances are I might have read the book already…Like the movie Shutter Island, I actually read the book years ago, or again, most Stephen King books.
If I’m not familiar with the source though, I’m always interested in knowing, and it’s easy to do online.
For things like based on an actual event, I always seek out the source, so then I can laugh at people who think that the mock documentation in The Texas Chainsaw Massacre is actual footage.
There’s such a world of difference when it comes to an actual event and the work based on it. It’s usually just inspiration, so much so that it’s worth informing oneself on the source.
I don’t watch much TV at all aside from The Simpsons and Xena. For The Simpsons it’s awesome though, because it’s fun discovering where all the satire comes from; political events, trends, stereotypes, it just never ends.