They are abundant free and would othewise go into the landfill/dump. So why not add them to the composter. I leave mine right in my garden beds to decompose.. of course only if they are free of seeds. In my composter I am hoping for volunteers to sprout and have pumpkins next fall, my kids would love it.
Lovelycherry

Pumpkins & winter squash take a lot out of the soil when we grow them; therefore, when I add pumpkins to my soil, I'm assuming I'm adding a lot of nutrients back in. So far this year, I've grabbed 6 rotten pumpkins that were put to the road by my neighbors.

Pumpkins are a green and they are moist... They add alot of moisture to pile and they decompose very quickly... and they are orange and beautiful. Pumpkins are cool.

Pumpkins are really nothing special - like most vegetables they're 80-90% water, in an unusually large container. But stacked free for the taking after Halloween they're irresistible, it's like being offered elephants for your zoo. Whacking pumpkins on a stump with a machete is a great past time. In the compost pile they nearly vanish, like fish.

Here is a link that might be useful: pumpkin stomp

What the others said, most people just throw 'em out. Heck I got one in a bag that had already mostly decomposed. I've been short of greens so punkins are a great thing for me.

I love to score pumpkins and squash but I feed them to my chickens and goats first. Then seeds are not a problem. Eggs have a richer color and I have plenty of manure to add to the garden.

I've picked up about 400 pumpkins since Hallowe'en. They make the best and richest compost we have when mixed with shredded leaves. We compost the seeds and everything. The moisture keeps the compost humming along. Pumpkins are big feeders..pigs..and all that nutrient goes into our garden. We compost most organics but pumpkins and shredded leaves are available in unlimited amounts and the two ingredients we can't imagine doing without.

My pumpkins provide a couple of months worth of feed for the chickens. They love them and carving into them gives the birds something to do.

Wayne

Worms like them too, so vermicomposters are always glad to have them!

Maybe they aren't really any better than any other produce we incorporate into our compost, it's just that they are so big and so available. It's a way of recycling them instead of loading up the trash cans.

Thanks everyone for the responses, now I understand more about it, :) Funny I never see anyone in my neck of the woods throwing out pumpkins though, :( but If I do, I'll grab them.
Alberta

Someone dumped a pumpkin on the property last year after Halloween and this fall I saw the pumpkin vine growing in that spot. This was nice but also humbling since the pumpkins I intentionally planted died quick or were eaten quick by critters.