They look bloody awful on nearly everyone. If you're too thin you look sickly if you're too fat...well...it doesn't do you any favours... very rarely does someone have those "perfect pins" to pull them off.
Wow, that one changed. I found a pair that actually fit me perfectly (topshop no less) a couple of years ago and I love love love. Esp. since I generally wear loose tops and my legs end up looking lost in wide jeans or trousers.