Terrible.
I keep hearing that Labradors, or golden retrievers, or chihuahuas actually bite more often than pit bulls. But the more important fact is that pit bulls maul people to death more than other breeds. Chihuahuas ... not so often.
I think little dogs are more prone to bite in general because they seem to be easier to frighten. But they also are easier to fight off if they attack you. Really who is scared of a ferocious Chihuahua?