@Kyle Suss
I agree. I think the geographical implication of a dealership trying to use global social media sites makes a lot of it irrelevant.
In a perfect situation, I think we would see OEM sites creating content that people would want to pin and repin creating a dialogue around a specific product that the customer would then find locally.
Personally, I have considered using pinterest as a way to find new ideas for blog posts or to share photos from a side photography business I have - mostly to try and encourage links to and from my site to interact with a larger community and raise my SERP.
As for the car business - I just don't see it being all that effective at selling cars on a dealer level.