I am fairly new to the ereading arena, but from what I can see the Pocketbooks have the most open format - that is one of its biggest selling points.
http://www.youtube.com/watch?v=UAwTc...eature=related for a Youtube video and
http://www.youtube.com/watch?v=ywRQV...eature=related for a video with information about Pocketbook as a company and its philosophies.