I booked the swim with the dolphins through Princess last July. We ALMOST had to cancel, due to weather - it was a torrential downpour. Princess would have refunded our money, but I can't guarantee that if we had booked it independently, if we would have gotten a refund, had it been cancelled.
BTW - it was worth every penny we paid. It was an AMAZING experience. The video afterwards is $50, but I didn't care if it was $100, I was going to buy the memories of this incredible and unforgettable encounter (we bought some pictures too).
Star Princess - December 2006
Adventure of the Seas - April 2005
Caribbean Princess - July 2004
Golden Princess - March 2003
Disney Magic - October 1998