No, the Rays are quite tame, they actually know and look for food, so they are very friendly, although the females can be huge, don't let that scare you like it did me. Its an awesome excursion, one well worth doing, have fun. Be sure to buy an underwater camera at home before you go.
Somebody on another board said that they got "bitten"......when they tried to play tug of war with a piece of squid. It really wasn't a bite, more of a hicky (I guess)........so, if you're feeding them, just let go and you'll be fine.
I was wondering because someone from Grand Cayman told a friend that people have been rushed to the hospital from being stung at Stingray city. Also heard that sharks have been known to show up on occasional. Just wondering how much truth there was to it.