In the competitive world of automotive internet marketing, it's hard sometimes to know what's really working and what's a waste of time. Too often, dealers and their vendors are led down a path to some new form of "marketing gold" that will help their search and/or social gain an upperhand on the competition. It's for this reason that I've avoided pushing too hard about Tumblr.
After using it for 3 years internally here at TK Carsites, I'm finally confident that it has 3 attributes that are important for anything that we are willing to recommend:
Wednesday, we'll be doing our first Tumblr-centric webinar called "Tumblr: The Most Powerful Automotive Marketing Tool (that nobody's using right)". It's from 9am-10am Pacific. If you're serious about your marketing, I recommend attending.
In the meantime, here's a video I did that highlights the basics of Tumblr.