Well, as you probably know, there are two parts to the rear window captioning system. One is the caption projector, which looks like these little scrolling message devices except that the letters are reversed like mirror images. The other part are all these thingies (sorry, not sure what to call these) that look like rectangles of plexiglas connected to flexible metal arms, the kind like you see on goose lamps. You insert one of these things in your seat's arm cupholder. (No idea how seats without cupholders are handled, though.) You're supposed to adjust the metal arm so you can see the letters from the caption projector reflected onto the glass.
It looks like a good idea on paper. But there were some issues -- it's not always easy to see the captions, especially if the moive image has lots of light colors at the moment. You could work around this by adjusting the glass so the captions are reflected against the dark area right under or above the screen, but that makes watching the movie difficult (especially if it's a big screen like in a stadium-style theater) since captions are a bit out of way. Plus, it may cause eyestrain in some people because the captions are close to your eyes but the screen is far away.
Also, a friend of mine wrote about her experience with rear window captioning at this url:
Rear Window Caption Display System
