Odds of someone having a flush on suited flop

[avisco01]

In hold'em, if the flop is three cards of the same suit, what are the odds that someone is holding a completed flush already? (Assuming the flop is all spades let's say, and I'm not holding one...)

[Jimmy The Fish]

You know the position of five cards, three of which are spades. That leaves 47 cards (10 spades) in unknown locations.

(10/47) * (9/46) = 4.2% that any specific opponent fropped a frush.