I read Divergent for my May book club meeting and saw the movie yesterday. There were some changes between the two which were fine. I'm not sure people going into the movie with no knowledge beforehand would pick up on a few things though.
The funny thing about the audience at 10:15am was the composition. Except for one guy it was teen girls and older women like me. Nearly all the older women had their bag of popcorn (like me) for themselves or to share with their female movie date. There were a few times when the teens gasped or made other noises to indicate their involvement. It was cute.