For once we disagree Simon. I think an armful to be the max, but very soon you will want to begin easing just 10-20cm before sheeting in again. It is all about feel for the boat and the conditions. Anyway, key is to not accidentally adjust rudder angle while sheeting the main.
I dont know how much the mast moves while sheeting the main going downwind and how that changes the spi shape. Never been in a position to study that.
Rolf, Are you talking about the main as in "an arm full"; if so I agree, I'd never suggest dumping the main in the gusts unless you want to buy a new mast...
I agree that sailing down wind and playing the mainsheet, you MUST stear carefully at the same time. I think the T medal race action from the Games where it shows Bundy putting the mainsheet in his mouth so he can still steer with one hand while playing the mainsail is a classic demonstration of sailing down wind 2 up.
