I think they started off like Chad explains and now are what Peale explains.
In Europe there even is a super-market chain called Coop. (they removed the - as well as the whole idea behind it I guess....).
I saw a US co-op on TV. There were two arrogant, over the hills girls who are famous and rich (Paris Hilton is one of the two) who are trying to do some work for a change. Well of course they don't really. It's more a show where they advertise their thoughts and feelings about normal people who need to work for a living.
Anyway, I don't know the name of the show, it passed along when channel-surfing and the girls would "work" at some ranch and the owner told them they had to buy some food for the animals at the co-op.
Of course they also came home with totally useless things (like a mega-big bird-house) like women tend to do....
I was actually pretty surprised something like co-ops still existed.
I also find it a very communistic idea for the US