Summary from a friends facepuke post:
In some states, if you see someone being reckless, you can contact the driver's license authority. A web form or a letter, describing the incident, along with the date, time, specific place, make/model of the vehicle, and a description of the driver. They have been known to contact the driver in writing, and at times, have made requirements of them or require a road test.
A dashboard or gopro cam footage would really get the authorities attention.