I will base the answer on my very fresh experience - I took the 70-516 (ADO.NET + EF in .NET 4) test this Tuesday and 70-561 (ADO.NET in .NET 3.5) last week and I passed several MS tests before.
I always prepared for exams. I take certifications as my personal goals because when I am preparing for it I always have to learn something new because I usually don't use about 30-50% of the tested knowledge. I like doing these certifications. My opinion about what these certifications mean in my career is described in another answer.
Despite the previous paragraph if I have a chance to check question and answers I will check at least few of them one day before the exam. Why? Because these exams are sometimes one big crap prepared by incompetent people and it is silly to not pass the exam when everybody around you will pass because they simply memorize questions.
I didn't read any questions when I prepared for 70-516 and I read a few of them when I prepared for 70-561. I think I know a lot about these topics, especially about Entity framework and Linq-to-Sql but that really didn't help me! In case of 70-516 30% of the questions would be marked on stack overflow as not a real question or we would ask for more details. That exam was terribly bad. Several times I read a question, I read the answers and the result was WTF? The correct answer was missing so I had to chose the best bad answer. In the other case I knew that multiple answers are correct in some cases but necessary details were not part of the question, etc. Simply the exam didn't test my knowledge - it was more about question wording.
Questions will also show you how far your study materials were from the real content. This was extremely visible in 70-561 where the self packed training kit didn't correspond to skills being measured in the exam!!! For example the book contains big chapters about Linq-to-Sql and ADO.NET Data services but these topics are not part of the exam and they are even not mentioned in the skills being measured. At the same time it almost didn't touch any implementation scenarios with MS Sync Framework but my exam contained 6 question targeting this knowledge really deeply. For the last, each exam contained some specialties which were not covered by the self paced training kits at all and didn't look like a part of the test's content. Commonly these topics targets COM or COM+ interoperability but in case of 70-561 it targeted SQL Broker.
I think this is whole commercial bullshit. If you check the preparation materials for MS test they will directly offer you some test sites. So what is the professional point of these tests and certifications if the minimal requirement for passing is: pay for the test, pay for questions and answers, memorize answers, pass the test, get the certification? Just be aware that this is not only problem of MS certifications - exactly same happens for any other product using this form of certifying. In the MS case this is going even worse because companies requires certified people for MS Partnership programs so employers even support this way of receiving certifications to have enough certified people.