The great thing about Blu-ray is that the OAR (original aspect ratio) is preserved. That means that for the following, you'll see this:
2.40:1, 2.35:1, 2:20.1 etc : you see black bars
1.85:1 : you will see a tiny bit of black bars
1.78.1 : full screen

The reason why this is good, is that the image doesn't get distorted: nothing is cropped off the sides and nothing is 'stretched'. You get it exactly as it was made, meaning that for some (most) movies, you have indeed black bars

Dark Knight has a shifting aspect ratio as the scenes filmed in IMAX are 1.78:1 whereas the other scenes are filmed in 2.40:1.

If you want your Blu-ray player to correctly display DVD's in the OAR of themovie, just make sure you turn off all zoom features on your HDTV as well as your BD player, otherwise it will still stretch and crop the image.


Lots of good and more technical info here:
http://forum.blu-ray.com/blu-ray-movies-north-america/5528-black-bars-4-3-16-9-2-35-widescreen-fullscreen-scope-oar-sticky-threads.html

thanks, great info and looking into that link.

-Robert