I went on a snorkel cruise in Cabo, they had a an open bar on the catermeran, which was well worth it alone. I dont remember the name of the excursion, but any of the ones that take you out to the arches to snorkel and then sail around should do. It was a good time.
Mazatlan, I only went to the tourist area of Mazatlan where the Hotel Zone, and we just did some shopping, and then had the best shrimp at the Shrimp Factory. Finished it off by going to Senor Frogs. I would also try to go to the Pacifico brewery for a tour.
Puerto Vallarta, we first shopped around town, and ate at a corner joint with a good people watching advantage point(dont remember name), then we went down to Chinos Paradise which is the best, along with LaJolla Mismalloya(bay). Beautiful and a great beach for sunning and swimming. I also used one of the hotel pools why I was there, just look like you belong.
Hope this helps, we had a great time, oh by the way, go to the Gigglin
Marlin in Cabo, and Hooters in P.V.
Lots of fun...