DD, my father and I took a paddle at a local state park this weekend - another three generation paddle. We took the same canoe that we did the weekend before - the 16' Wabnaki. We paddled a complete circuit of the pond and we saw many, many boats - easily 3 dozen boats. There was an inflatable, a few other canoes, but by far, most of the boats were small plastic rotomolded kayaks. We were the only wooden boat on the water.
Plastic boats certainly have their purpose. They're durable and take an incredible amount of abuse. They're also inexpensive. Because they are inexpensive, more people can afford to buy them and provide an easily accessable way to start paddling. Their shortness, "cute"-ness, bright crayon-like colors and low cost seem to be instrumental in making them popular.
There are some downsides, too. They are not always easily repairable. Some of them have bottoms which oil-can (Flopping up and down.) which effects paddling efficiency. Scratched up, they can look pretty horrid. They tend to be wide for their length and sometimes track poorly as they are short. Because of the roto-molded construction, they tend to be heavy - often 40-45 pounds for a 11' long kayak.
At the take-out, my father helped two women with these little plastic kayaks put them on their car. He was stunned to find that the little 12' long kayak weighed nearly as much as the 16' cedar-strip and 'glass canoe that we'd been paddling.
I really prefer wooden boats, but I can't disparage the plastic boats. (at least not too badly...) They introduce a lot of people to boating who otherwise might not get the chance. Getting out on the water is important. You have to start somewhere. Also, because of their limitations, they often lead people to better fiberglass, Kevlar, or wooden boats. I'm often surprised at how many of my students in my canoe-building class have started in little plastic kayaks or canoes.
However you do it, get out and paddle.