In 2009, after a banker gave incriminating details to the Internal Revenue Service, Swiss bank UBSreached a settlement with the Department of Justice by paying a $780 million dollar fine and disclosing the names of US account holders to the Internal Revenue Service. Because of possible violations of Swiss banking laws, the Swiss government had to participate in the settlement.
Earlier this year, a former banker in the Cayman Islands for Julius Baer Group, Ltd. gave stolen records about overseas accounts to Wikileaks.
Both bankers are expected to file claims for substantial rewards - possibly in the billions of dollars - under the federal whistleblower program. The IRS is expected to promote this program, especially for foreign transactions, over the next few years.
Here's a good, short summary of the program - for both potential whistlebowers and potential "whistleblowees".