Google Research comment...
Jeff you give great information, and I love the site. I hope my comments are seen as supporting, and cautionary, and not argumentative.
I am not saying I agree or disagree, but what I would like to do is make a recommendation to all readers to not assume everything you read with a "research" tag, coming from a specific company, or research paid for by a company, is fact. Don't always believe all the "research" you read from a company that is eager to get advertisers to start spending money in their medium. Of course they want buyers to think the results will come sooner rather than later.
In my opinion, there are just way too many variables to a dealership's adWords (or any PPC) campaigns, for turning clicks into sales, to put a blanket statement on when 70% of searchers will buy... seasonality, market, market location, competition and so forth, are just a few of those factors that would move that percentage and that times frame significantly.
Example:
I worked for one of the three top major travel websites. Just like everyone else, I saw the TV ads, with the "independent" research firms, talking about 50% less than Expedia, or 33% better than Travelocity, or 25% better than Orbitz.... What I learned is that those websites PAY the research firms to do a study on the website's selected markets, that they know they have worked deals to have better rates. They know they can't lose.... but people take it as fact because it is "research". What it is really is marketing...