I recently observed a hand I folded preflop. At the turn, the table was TJQK rainbow. Two players are left, and they cap it. I'm of course thinking they both have an ace and that it's going to be a chop. On the river, one player bets and the other just calls, obviously thinking the same. As it turns out, the guy betting the river has a 9, while the one just calling has an ace. While this doesn't happen very often, I think in the long run you'll be better of capping, simply because other people do stupid things.