One of the major perks to owning a cat over, say, a dog or a horse, is that all cats instinctively drop their waste into neat little litter boxes, eliminating the need for frequent "walkies" and the palpable awkwardness that comes with the public use of pooper-scoopers and plastic baggies. Cats instinctively seek to bury their droppings, so it works out for everybody.
Contrary to popular assumptions though, this behavior doesn't come from Snowball's obsessive compulsive cleanliness, but rather an evolutionary holdover from before felines were domesticated and had more dangerous predators than the vacuum cleaner to worry about.
Burying the poop prevents detection by their enemies, but there's another layer to it, which is that they do it to avoid challenging the dominant cat of the group. It kind of makes sense, if burying the poop is a sign that they fear another, larger animal, then leaving it uncovered would be a pretty aggressive act. "No one here is bad enough to fuck with me. Enjoy my shit."
So... what do you suppose it means when your cat doesn't bother to cover his poop?