i have been reading several WW blogs and following a couple successful people. Both of them have recently posted about incredible psychological effects; one says she realized life was a little harder because she couldn't hide in her fat, she was right there on the surface and felt more exposed within less body. She's not full of new-agey hokum, but that was the gist of her explanation. The other one was talking about not having a buffer between herself and the world. Both after really large losses, 80lbs and similar.
Here's one: http://msbitchcakes.blogspot.com/2010/10/emotional-effects-of-reaching-goal.html