A number of doomsayers predict that the coming of "peak oil" will cause worldwide economic disruption. Others, including Amanda Marcotte, look forward to a future where our corrosive commuter culture is undermined by the high cost of fueling cars, and where incidentally we'll be generating fewer greenhouse gasses. I would love to see those sorts of effects myself.
Sadly, coping with the absence of oil doesn't require new, blue-sky technologies. We've known how to do it for 80 years. Estimates I've heard put the point at which FT is an economical competitor to oil at around $80 a barrel. Even if that's too low, it's pretty clear that it's not at a level where switching over to coal as a way to power cars would result in widespread reduction in use of cars. And any reduction in greenhouse gasses which might come about from more efficient cars will likely more than be made up for by the energy requirements of the FT process itself.