[wulf]

I think it is fair to say that the focus and recompose method becomes increasingly problematic as the DoF becomes narrower. If you are in that range where the eyes can be sharp and the tip of the nose soft a small amount of repositioning could throw you out. Arguably though, you might be better served by stopping down the aperture a bit anyway because that blurry nose will probably detract from the result even if the eyes are perfect.

It is definitely worth learning how to switch between your AF points (easy on the D40 because there are only three of them!).

Wulf