Customer = organisation (e.g. Tesco) that buys from a manufacturer. Buy lots of product and have a direct impact on profitability. Think one to one, two-way conversations. Think capital C.
consumer = person who buys from a Customer. Buy small amounts of product and have an indirect impact on profitability. Think one to many, one way communication. Think small c.
One of the impacts of the social web is that manufacturers are having to rethink their attitudes to consumers. Consumers may still buy small amounts of product, but they can make a lot of noise, and expect one to one, two-way conversations with brands. Manufacturers need to think capital C when it comes to Consumers.