When I think of interpretive communities I have to say one of the biggest ones that pop up in my life are in connection with Lord of the Rings. Most of my friends already know it's one of my obsessions in life.
There are actually two levels to this group. There is the much broader level which includes everyone who has ever watched any of the movies. Here we can compare characters we like an dislike, take about out favorite parts, and makes jokes about why the eagles don't just fly them the whole way to Mount Doom.
The smaller more intense group is those who have not only watched the movie, but read the books as well. These people can share in the same discussions as the larger group, but they know more of the details, parts that are not in the movie which are just as epic. These people know that the Eagles didn't fly them the whole way because they are independent creatures and would never subjugate themselves do such things. They also are not really friends of the Dwarves as suggested in the movie.
Anyway as you can see those who have seen or read Lord of the Rings are part of the interpretive community, complete with their own set of jokes and inside references.