Today I stumbled across this pet column, which is pretty amusing.
My favorite is this:
"I've always said guys would rather not clean up," says Nashville-based feline behavior consultant Pam Johnson-Bennett. "Kittens can often be a bit much to deal with. I suspect that Suzy's hanging around the box, and her mere presence may rush (the male cat) out. Either that, or while they do get along, Alexander still wants to leave his mark, saying, `this box is mine.' He leaves this marker by not covering up. And, as a matter of practicality, it's very normal for one cat to cover what another has done."
That's what I like about cats - they bury their crap, or even the crap of a friend.