Bad news: my macbook pro did not work with the projector, period.
Good news: I have seen it do this before (in a room with several mac experts -- it was not user error) and brought a backup laptop.
Bad news: I forgot to include the django beta1 framework in my code upload, so I told people to just download it. But beta2 was out, and didn't work with the version of App Engine Helper I had. (It looks like r58 fixes this.) Manual poking about the django download site ensued until I got a new zip uploaded.
Good news: the conference organizers liked it anyway and asked me to present a second time later in the day. Everything just worked the second time around.