The three foul rule is a good one, and it requires great skill to get an opponent on three, but at high levels of play, it rarely arises in the modern game. Years ago, the levels of kicking, jumping and masses were lower across the board than today, and three foul wins were more common. Now, the top guys are really good at all three, so it's near impossible to get them on three.
If I had to take a wild guess, I'd say that in top pro play, about one rack in every 200 is won with the three foul rule.