I did one in Cancun a couple of years ago. Got to swim with five dolphins with just myself, a friend, and a 13 year old. It was so fun! They are kind of like big Labs. Constantly vied for attention and petting. Strangely enough, they have attitude about certain people. They LOVED the 13 year old girl and liked me well enough, but for some reason, they didn't like my friend and only interacted with her on command from their trainers. They finally had to give her a fish bucket so they would go near her voluntarily. Anyway, we spent about 30 minutes swimming in their pool and then another 30 minutes doing "tricks". Got to do even the neat thing where you lay on your stomach and flex your feet. Then 2 dolphins push your feet with their noses really hard and you fly across the length of the pool. The cost was $125 and we were at Xcaret. There are alot of these programs in the Cancun area but I was very selective. They are environmentally conscious but they don't seem to have many regulations concerning the dolphins. There are some real crappy conditions in a few of them.
My next goal is to dive with them in the wild....