During yesterday’s afternoon session focused on Auto at Drilling Down on Local ’08, the panelists nearly universally said U.S. automaker giant General Motors was the furthest along in figuring out how to leverage the Web.

Mitch Golub, president of Cars.com, said that has not always been the case — Toyota used to be the leader OEM but has since ceded that post to GM. GM’s leadership on the Web did not do much for driving car sales, as Ward’s Automotive reported that Q1 sales were down more than 16 percent. Ward’s Cliff Banks predicted that there’d be perhaps 1,000 or 1,500 fewer rooftops (auto dealerships) by 2010 as undercapitalized dealers find the economic downturn too difficult to navigate.

As the economy slows, dealerships and OEMs will push even harder to ascertain the true ROI of their media mix, which should ultimately benefit the online sector.