I passed all three exams and I must say basing on my experience (I have now about 30 MS exams passed, so I think my opinion might be worth something) that they are generally easy (I think, too easy) and still very raw. Some comments:
70-236 is really focused on EMS, but the incorrect answers are not so well selected. Many questions can be easily answered without even reading the question itself, because all the answers but one are obviously senseless. It could have been made better challenge.
70-237 is by far the easiest test of the three. The big complaint is that it covers very narrow area of expertise. There are lots of questions almost literally repeating each other, and some important areas (I won't be more specific here in order to not violate the NDA) are not covered at all.
70-238 is the hardest exam mostly because the questions are long and need real attention when reading, since small details matter. But what is really sad here - there are questions badly formulated or just simply incorrect statements. I will not quote, but the statements like "You install an LCR cluster" or "you install Exchange 2007 on 3 computers: Exchange 2007 server, Client access server, and Hub transport server" are frustrating when you really try to understand what the question was.
I wish the test writing team could have done better job on this exam.