plhorn, there is no generic rating... they vary widely.
Enforcement varies state-by-state, but they do not necessarily have to follow the Coast Guard rating, which is the posted capacity on your boat.
Brett nailed it for Washington state... it's completely up to the officer and whether he believes you are overloaded, which blows my mind.
I don't support overloading. That being said, at least in Washington, if you are being responsible out there and have enough life jackets for everybody on-board they will generally look the other way...