Janet Street Porter made an interesting point about supermarket employees. Those on the tills tend to earn less than those in the storeroom - both unskilled jobs.
Women tended to work on the till whereas men in the stores. Perhaps women were better suited to the tills because they (arguably) have better customer service skills (able to chat and smile and whatnot) whereas men can move stuff about quicker.
Is this a case of gender pay gap?
Even if it is I'd still rather work in the stores than on the till, whatever the pay.