The story is, according to 'Hard Drive' by James Wallace and Jim Erickson, that Bill Gates and Paul Allen were in Gates' 911 and were pulled over for speeding. Gates had, at some point earlier, taken the Porsche back to the dealer complaining that it only went to 125Mph, not nearly as fast as the manual specified.
The officer hauled Gates to jail as Allen and Gates were playing games as to who was actually driving at the time. As Gates was the owner, he got booked. Bail was posted at $1000. Gates probably had that in his spare change pocket at that time.
Gates was tailed by police for several days after that as the police couldn't believe that someone so young could own a car like that, have so much money and run a legitimate business.

It may comfort you to know that Gates did actually lose control of the car once. He and Chris Larson were taking a 3am break and were winding through the desert alon interstate 40. As Larson describes it, "we were doing 120 forwards then 120 sideways."
Neither were injured and the Porsche only suffered minor bruises.