My husband and I were in Cabo Pulmo with the intentions of diving for 1 week in mid July, 2011. In retrospect, it was not the best time to go...as the visibility was not very good at that time of year and the diving shut down for 2 days because of a hurricane further southwest of Cabo San Lucas.
Anyway- here is what I can tell you about Cabo Pulmo and the diving there. Getting to Cabo Pulmo is very difficult to do without a car - so renting a car in Cabo San Lucas is best and most affordable.
Cabo Pulmo is a tiny village, and the diving is limited to 2 dive shops (at least when we were there last summer, that is all that we could find). We went with Cabo Pulmo beach resort dive shop. They were excellent - the divemasters were very experienced, safe, knowledgable, and thorough. The equipment was also very good. The BCDs were in good shape and they had many sizes. The regulators were excellent quality and well maintained. They also had a variety of sizes of wetsuits and they were also good quality, not ripped or falling apart. My husband and I brought out own masks.
There were 8 divers in total in our group. We dove 2 dive sites before we had to head in because the sea was so rough and the visibility was terrible. We did not see very much in the way of underwater life - but I think much of that had to do with the poor sea conditions, and the time of year (the migrations of whales etc had been a few months earlier).
My husband is a very experienced diver (500 dives) and I am not as experienced (100 dives). My expectations were high as we had been diving in the Red Sea, Borneo, and Mozambique and were looking forward to huge biodiversity in Cabo Pulmo. After speaking with the dive instructors, they said that the diving is good, but not as good as in Asia or in the Red Sea. If you get good visibility, then it will certainly be great!
We were the only people in the dive group who were staying in Cabo Pulmo. The others came up for the day from Cabo San Lucas with a dive package that they had arranged with their hotels in Cabo San Lucas.
There was not much in the way of food in Cabo Pulmo - there was a very small grocery store which had some dried goods, bananas, tomatoes, onions and potatoes. The restaurant at the bungalos/beach resort was excellent - but expensive. You can bring food in from the closest town that has a good grocery store. The bungalows have refrigerators and stove tops in the rooms. It cost us approx. $90.00 USD/night without air conditioning. The place runs on solar power, so air conditioned rooms only have the air conditioning available during the day (there is not enough power to run them at night, but there is enough to run a fan).
I hope this gives you some information about Cabo Pulmo. We did not know very much about it at all before we went, and found that it was hard to get any reliable information. I would try diving there again, but not in the summer!!