I haven't, but I know quite a few people who have checked references and gotten a negative response - in one case derisive laughter followed by an incredulous "

I haven't, but I know quite a few people who have checked references and gotten a negative response - in one case derisive laughter followed by an incredulous "Really? They put me as a reference?". Obviously it depends on whether it's a big shop where you'll get HR stonewalled, or a smaller place where you'll have the owner or a coworker.