...adding to my above post: also the amount of graphic detail in any given shot/film DOES effect the size, becuase in VBR encodings (which is how most flicks are encoded) it will cause the bitrate to spike in order to accurately represent any increase in details on screen. This is especially prevalent in shots with smoke or snow. So if you have a pretty static film with a bitare set to be between 10-40mbps, it will spend more time hovering around 10mbps, and thus the overall size of the film will be smaller. Have more detailed scenes, and... well, you get the picture. If you have a PS3, have your status screen up when watching a BD movie, and watch that bitrate dance!