Re: Kayaking
Sit-on-Top's are fun and, because they are generally much wider than a traditional kayak, less prone to tipping when the passenger makes a dumb move.
The problems with them are; 1) much heavier for any given size, 2) no weather protection for the occupant as you're exposed to the elements 3) no or limited gear storage - cameras would die a sudden death and 4) no protection at all from potential beasties of the sea such as the numerous jelly's in the ocean with their stinging cells.
I've played on a couple of models of sit-on-top's and enjoyed them ... the fishing from them was great! Even considered purchasing a 12' model which included a live well for bait. Sun screen by the quart was manditory in Florida.