Using powerful data mining software, banks and other industries have weeded out less profitable customers or singled them out for higher fees. On the other hand, they target their best customers for pampering. Already, about half of big banks with more than $1 billion in deposits use profit data to make customer decisions, more than double the percentage just a year ago.

For banks, the most profitable customers are those who keep several thousand dollars in their accounts, use a teller less than once a month and hardly ever use the call center.

Banks have been forced into this strategy because they are under attack from brokerage firms and mutual-fund companies which are trying to woo away highly profitable bank customers.