We were on the Boobs Cruise for my birthday on the 17th. It was outstanding! If there is one scheduled while you are there, BostonMel is right...book it! You'll have a blast. There are other day trips to the Isla but this is the one to be on. We met people after the Boobs Cruise that said "well damn looks like we got on the wrong day trip to Isla..." Really hoping for one during our return trip. Fingers crossed!
We have always wanted to do the Cenote Tour, but have a hard time prying ourselves away from the all-inclusive sexy pool. We have done the Jungle Tour (4 times), Captain Hook Cruise, Isla Mujeres Day Cruise, and an old school Booze Cruise back in 2001, here is a picture from that booze cruise over 10 years ago (obviously not the Boobs Cruise with all the clothing):
The sexy pool is far too hard to leave so I am going to practice my diving in the hotel room instead .
If you go with Boris he supplies all the gear that you need (apart from a wet suit). Boris is the Canadian guy and works from the same place as where you get the towels from. I got certified by him and definitely recommend him.
The cenote tour sounds interesting. what is the captain hook like. This is our second trip and I almost went diving the last time, but just decided to stay that the resort.