I am constantly amazed at the innovations and inventions that Americans have come up with that we all take for granted. This is one of those.
Much of my highschool weekends were spent going to the Barrie Triple Drive-in (Ontario) with a 2-4 of brew in my buddy's Chevy van.
Even before that my parents would take the family and go to some of the 5 or so drive-ins that were in and around the Toronto area.
Childhood memories included playing on the swing sets waiting for dusk and the anticipation of the double bill movie (usually a lame Disney flick - I seem to recall such as That Darned Cat, or Bedknobs & Broomsticks) and the cheap food (fries and pop).
I did take my girlfriend to see some when I was older - Heavy Metal, the 4 movie Horror-Rama (Boogens!, Prom Night, Terror Train...and I think we were steaming windows most of the time). And yes, we could fit 3 people in the trunk of an Olds Delta 88 (1979 model).
Little known fact: until the 1960's there were no drive-in theatres in Quebec. It wasn't until the Quiet Revolution, that the religious control of society gave way to secularization and these types of theatres became acceptable. (this is from my Gr 10 History).
At present there is a new Drive-in theatre (double screen) that just opened in Toronto, at the Docks, right downtown by the harbour:
http://www.toronto.com/movies/listing/100067