You would be amazed at the people who still try to cheat even when you have different versions of the exam and have spaces between seats. I proctored general chemistry exams at my undergrad and people would discuss answers on the exam. People even tried to trade exam forms when they were passed out so they could be next to someone with the same exam.
One of my friends was in a biochem class last spring, and the professor has 3 different exam forms. These two students (who have been known for cheating apparently) always sat next to each other on exams. The TA who was proctoring the exam apparently pulled their tests aside when they were turned in because they suspected these two students were cheating.
They had different exam forms. They ended up getting the same score. They missed the same questions. And somehow their essays turned out to be as close to identical as you can get. They didn't get caught because the professor was not proctoring the exam and he did not catch them in the act. Apparently having the same exam grade and same essay, and missing the same questions isn't enough proof.
It really is a shame because its not that these two students aren't intelligent. They scored decent enough on the DAT to get accepted to dental school. They are just lazy. I just wonder if they cheat in dental school too. If they do, I'm sure it will catch up to them eventually.