I saw in the news today that eBay Classified ads can now be linked to Facebook so this is a medium that big advertisers are embracing. Benefits outlined are below:

For buyers

Facebook Connect will increase your confidence about buying online. Facebook Connect gives you an instant introduction to the seller via a visual profile attached to their ads.

For sellers

Facebook Connect will give your ads more exposure by posting them automatically to your wall. Plus, the visual profile attached to your ads will make them friendlier and more personal to people who don't know you.

Logically, the same benefits would accrue to dealerships. I heard of one company recently (TriZangle) that will even put a dealers entire vehicle inventory on Facebook. It appears that "just having a dealership website" may no longer keep dealerships on the leading edge.