My 9-yr old dog has never bitten anybody. She's really not around many people, though. She'll bark her head off at ya, though.
Anyhow, when we have her outside she is always, ALWAYS on a leash. Sometimes people on a stroll will see her and want to approach her with "awwww... she's so cute! Does she bite?"
I always answer, "well... she's got teeth". I don't THINK she'd bite them, but she's a dog. I can't guarantee she won't bite them just because she's never done it. Overall she's not a real friendly dog and I tell them that. She's persnickity about who she likes and who she doesn't. Now... if they stick their hand in front of her face... then they're just stupid after I've warned them to reconsider.