Bumping this, not because of the OP, but because I love the idea of certain animals occasionally stealing things off the ground. (Also DF is awesome.)
Raccoons and monkeys (do we have monkeys?) might actually steal small items, and others would take certain resources (meat, bones, carrots...) depending on what they would normally eat. Omnivores should have a preference for prepared foods.
It wouldn't happen very often and unless a raccoon got a hold of a key or something it shouldn't be too annoying, it's just give people something to RP off of.
Also, since this was brought up earlier, I've heard of several cases of deer attacking people in real life. Heck, just search for 'deer attack' on youtube and I bet you'd pull up a ton of results, and that's only the ones that've been caught on video.