I came across a pretty cool site in my browser's bookmarks that I had long ago saved and subsequently forgotten. Michigandriveins.com lets you explore the few current drive-ins still in operation as well as the drive-ins that are now closed, in pieces, or gone altogether. I find it neat to see a little piece of Americana from Michigan's past. Some of these drive-ins were quite impressive with small scale kiddie trains (the Bel-Aire in Detroit) and some were only in operation for a couple seasons (Constantine Auto Theater July 1948-September 1949).
Anyway, it is a pretty extensive site with photos, old ads, and current pictures showing the decay of some of the theaters and the longevity of the few still in operation. They even have a section devoted to drive-in restaurants both past and present.
WARNING! You will spend a long time at this site. Taking a peak at the past and the "good ol' days" that are now gone is incredibly time consuming.