I dislike open book exams so much that I took nothing into my last one. It was a unit without much memorisation that focused much more heavily on applying concepts, and I feel that having it as open book was a trap for ill-prepared students.

One of my highschool teachers mentioned that a book wouldn't help much before her first open-book test, then openly stated that afterwards that it was a small trick to see who wouldn't study. She was among the best and most-liked teachers in the school.