I do think if you loose it nice and slowly like on SW then you are giving your body everychance to avoid loose skin as much as possible , although if you loose A LOT , then most people will have some , and to me I would much rather have loose skin than be huge !!
I lost 7 stone in 6 months , and my skin is pretty good , I ave a bit of sag on the bottom of my stomach , but I also have 2 kids and had 1 c section , so would probably have it anyway , and the tops of my thighs are a little 'ripply ' but it is improving .
It can take up to 18 months for your skin to catch up , my boobs shrunk from a 42 DD to a 36 B , and were quite 'saggy ' but in the last 12 months they have perked up no end ( my husband is very relieved !!!)