My family in maine uses Honda ATVs for a variety of purposes on the farm, from sustanably harvesting wood for the winter (leaving behind younger and older trees) as well as sustanably harvesting larger trees for lumber to transporting recently harvested apples to the grinder for making cider. For my family they are definately a tool. While we also own a sea-doo it sees little use, spending most of its time on it's trailer in the barn. That was purchased as a recreational toy for getting to the best fishing holes. The engine free canoe sees far mroe use than the sea-doo- it doesn't need a trailer and can be tossed on top of any of the cars to get to where we're going.

sea-doo's are popular for the same reason sex is popular. Its fun. While I don't really use my Polaris (sorry just had to plug a better jet ski ;-)) that often because its a pain to get in the water and has to be cleaned out all the time. I do have to say that your description of jet ski's (bombardier made them but kawasaki made them popular) could also apply to recreational boats especially most yachts, sports cars, roller coasters, video games etc. all of which provide little to no productivity but provide entertainment.