Milestones 

I'm looking for the source, but IIRC, the Super Cub became the #1 motor vehicle in about 1997, when the total a was about 25 million. That's probably the most significant milestone. In 2008 was when the numbers totaled 60 million. One (weak) source I saw said it was 65 million as of 2010, not surprising given current production rates. It's somewhat trivial, but it would be nice to nail it down if we can.