I went to one locally and lost 23 kilos, this was about 5 years ago.
Like Tinks there were a lot of older people at my meeting who were there for the social aspect, but the younger ones who were there (and some of the older ones) were really focussed.
I think it also helped to motivate the member who had been there longer.
They did have some weird rules, like the person who gained the most weight had to take aoty pig home..that one went out the door though..