Every holiday meal my Grandma would make several Jello dessert molds, which I always ate right up. You could count on finding at least 10+ boxes of said "food" in her cupboard at any given time. It is fascinating what we will eat when we are children...perhaps it is more amazing what people will continue to eat as adults when they have the ability to make choices for themselves and understand exactly what they are using to fuel their bodies.
Now, Kraft has a very glossy website detailing their Jello products, but, surprisingly, nowhere (that I can find at least) do they state what Jello actually is made of. But it does include this in its history section:
"During the early quarter of the 20th century, immigrants entering Ellis Island in New York City were served JELL-O gelatin as a 'Welcome to America.'” Nothing says welcome to a new home like desserts made out of animal bones, tissues, and other tasty treats!
Wait, so what exactly is gelatin? "It is derived from collagen found in the bones, cartilage, connective tissue, and skin of animals, traditionally cows. Most commercially produced gelatin nowadays is produced from pig skin. If you have ever roasted a chicken or ham, you made your own gelatin. The juices in the bottom of the pan contain gelatin rendered from the collagen, and if you put the roasting pan in the refrigerator, you'll find some of the juice setting into a gel."
Oh, and the Jello site also features a "Flavor Finder." Hizzah!
Jello is certainly the most famous gelatin based product, but I'm sure most people have no idea the sheer number of products that use it. I can't find a great list, but here is a decent discussion - Yahoo Answers. Just look at labels when you buy things, especially candy. I used to work in a cafe and would entertain myself by reading the labels of the food we sold, and explaining to my coworkers what exactly was in what they were eating. I was not being mean and never told anyone not to eat anything - I simply told them what they were putting in their bodies. This led one girl to storm out of the cafe yelling at me, "YOU RUIN EVERYTHING!" Unfortunately I'm not the one who filled the foods she eats with shit. Ah ignorance.
For vegetarian alternatives to traditional gelatin, check out this article.