Well we have a decision from the FEC on whether Sen. John McCain broke the rules when abruptly backed out of the presidential public financing system for the primary race. In a widely anticipated move the six commissioners at the Federal Election Commission voted unanimously to sign off on McCain's opt-out.
It's possible McCain could have faced heavy fines for opting out of the public financing program after accepting funds. However, when he made the decision to back out of the system the FEC did not have a quorum of commissioners to rule on the decision (the Commission was more or less in recess for many weeks while the Senate wrangled over nominations for vacant commissioner seats). Subsequent questions were raised about whether McCain has used public funds to secure a loan for his financially shaky campaign, but the FEC has ruled that nothing improper was done.