first time when i encountered open book exam was in sec1. that
time the whole class felt so happy la when the teacher said you can
refer to your textbook during the exam.
then in the end, no one study for it. coz can refer to textbook
ma.
hahahaa. big mistake. because you have to be really familiar with
your textbook to find the answers quickly. it's really very hard
la! the time so short some more! and so many questions!
so the next times when we had open book exams, we would still study
our textbooks. but it's very hard to score!! competition is tough.
questions are really hard too.
so i dislike open book tests.
closed book tests studious and hardworking types will have an edge
over those who don't try hard or with poor memories. and teachers
are sometimes more lenient when marking too. questions aren't so
tough. 
and i think it tests
your knowledge more?