We have always said it is perfectly possible to have a (high volume) cafe where customers can serve themselves .... until the till. See how the Donq bakery has now sorted this out at http://news.bbc.co.uk/1/hi/programmes/click_online/9761797.stm using software recognition equipment.
Only relevant to the larger cafe and where queuing is a potential problem but the elderly and the disabled do cope and some actually prefer to serve themselves.