I know a guy who knows John Carmack. That's because two degrees of separation is probably about the average in our industry - if somebody linked up the "Six Degrees of Kevin Bacon" server to
Mobygames instead of IMDB, that might be what we find out. This has an interesting side effect: if you're looking for a new job, somebody at the place you're looking probably knows somebody who used to work with you. So if you aren't careful, "You'll never work in this town again!" might be a very real possibility...particularly if you managed to piss off a hub - one of those people that everybody knows.
Side note: if you badmouth somebody to a prospective employer, they can sue you for defamation of character. The only thing it's legal for you to say, as I understand it, is, "I would hire him again," or, "I would not hire him again." Unless you trust that prospective employer not to reveal their sources...mua ha ha.