For the first time since upgrading to Lion, I watched a movie through Apple DVD player (previously ripped movie) on my external display (an Epson 1080UB projector). I normally do this on Snow Leopard with no problems. With Lion, full screen was only possible on the primary display - so I had to make the Epson projector my primary display and then watch it. What a pain!! I have filed a bug report with Apple.