Americans' trust in banks has fallen to a record low, with only 21 percent saying they have "a great deal" or "quite a lot" of confidence in them. That discontent could spur some to action. A new survey from Javelin Strategy and Research found that 11 percent of customers say they're likely or very likely to switch their primary bank over the next year.

Big banks, moreover, are the most vulnerable: A quarter of all Citibank customers say they're likely to switch banks, and 21 percent of Bank of America customers say they're willing to do the same. New fees were a particularly notable complaint, Javelin says.

(Javelin Strategy & Research)

What's at stake for these banks? The customers that say they're likely to switch banks hold an average of nearly $30,000 in deposits — "30% higher than the balances for customers who indicate they are unlikely or very unlikely to switch," Javelin says, amounting to $675 billion overall. It's not enough to bring down any of the biggest banks, but it could put a dent in their retail division.

That said, Javelin points out that the convenience of big banks — lots of branches, ATMs, online and mobile banking services — often ends up trumping customer dissatisfaction. Just 3 percent of customers transferred their money in the last quarter of 2011, when Occupy Wall Street and other activists made a big push to support "Bank Transfer Day."

"To compete, regional rivals, community banks and credit unions must smartly prioritize investments in technology that redefines personal banking and personal security by sharing control with customers — with an urgent emphasis on mobile banking and mobile deposit," Javelin concludes. Younger customers, in particular, could be particularly persuaded to switch over: More than half of those who transferred their accounts since early 2011 have been under 35.