Where should randomness be inserted into ball movement physics?

[smbhax]

They don't really need to work too much on the look of the ball spin. Ball spin is not readily apparent in real life by looking at the ball except at low ball speed (movement speed not spin speed). Spin has a subtle effect during much of play but at times it can make a significant impact on game play. I think it will be very difficult to get that subtlety in a game.

Oh, well nobody said it would be easy. FarSight themselves said they've tried it a few times in-house and haven't managed to get it looking quite right yet.