Well, if you listen to the poker sites, they all have anti-collusion mechanisms in place to stop this sort of thing. Hand histories, which can always be looked at by the poker sites can reveal collusion. It would take a lot of time and effort to make collusion profitable.
I've seen suspicious things at Sit-n-go's, where one player at the beginning calls off all his chips with an unbelievably atrocious hand and doubles up another player. However, when you realize that as far as SnG tournaments, the colluders must pay 2 buy-ins, it really doesn't seem like too much of an advantage to me.