Jiffymom when is your cruise? Mine is on the Carnival Splendor May 2010. Anyway for Puerto Vallarta I was thinking of taking the water taxi to Yelapa I think it's about an hour by water taxi.
Here is a thread I started on the chit chat board. http://www.cruisemates.com/forum/viewtopic.php?t=611746
Yelapa even has a waterfall, however, during the dry season it isn't to impressive.
But during the rainy season it's pretty nice.