I definitely remember them. We had a few around the Boise area. The last major one survived up until somewhere in the early 90s. In fact, one of the last movies I can remember driving by and seeing playing on the main screen was Batman Returns. Then it stayed abandoned for a few years (though they did have a regular theater at the front of the property that survived for some years longer).
Dang!! So I found it using the Historical Imagery slider on Google Earth. I totally forget they had a second screen that was around the corner from the main drive-in. Crazy peering back into time.
I always thought they were fun. They just kind of had a vibe to them. There is one still running in Caldwell (a suburb of Boise) and I believe there is another one in Parma (a little ways outside the Boise area). I've been meaning to go one weekend for fun, but just haven't yet. Maybe this thread will reinvigorate that idea.