I think a lot depends on the elasticity of your skin and how young you are helps in this respect . However, I don't think anyone who has lost a shedload of weight can avoid having loose skin afterwards due to the skin having been stretched to a such a great extent. I don't think any exercise in the world could help restore skin back to it's original shape as exercise tones muscles and not skin. I have lost only 15.5kgs and am nearly at my goal weight. It is not really a lot considering, but I have loose skin particularly on my thighs and belly, which nothing short of surgery will help. But then, I am middle aged, and that has a lot to do with it I think, due to lack of elasticity. If I was 20, I don't think I'd have this problem.
SW: 76kg (08/07)
CW: 60.2kg (21/05)