I think a good balance is what CompTIA did on the Security+ exam. They'll show you the focus areas you missed questions. For instance, I believe the language is, "You missed one or more questions in the following areas: " which while they don't you the specific question, can point you to where you had issues on the test. If you have a weakness it may not be a particular question but a weakness in that general topic. It's a good balance between giving a test taker some knowledge of weak areas and protecting the exam.