Stevens posts weekly on Facebook, and his latest update is an essay asking what is the point of concept cars. He starts with Norman Melancton Bel Geddes' 1933 Motorcar No. 9 and works his way through General Motors' 1939 Futurama pavilion and traveling Motorama exhibits, the coachbuilders of the fifties and sixties, throws a Ford Probe III concept in from the eighties and alights on the Porsche Boxster concept.
He doesn't wrap up the piece with the answer, but lays out various reasons for why concepts come into being. And if you're into automotive design, check out his Facebook page photo album for a ton of car photos and the occasional caption.