Paper: among characteristics not mentioned, <i>where a passage occurs in a page</i> (or how far within a book or article) is part of the context, and I suspect that human's spatial memory comes into play with this. Online infinite-scrolling content lacks this particular clue, and even PDFs only offer the "where on the page" vs. "how far into the book" aspect. I can also often remember my place in a book simply by staring at the page number and committing it to memory -- at least for a few hours or overnight. Though bookmarks are useful.<p>Electronic: Over half a century into the digital age and I think a significant problem is that we still haven't settled on the "right" format for real information consumption. There are plain-text documents, simple HTML, word-processing formats, postscript and PDF documents, and now eBook formats. Absent its lack of text search, ghostview -- 'gv' on Linux -- is still one of the best reading clients I know of, particularly in how it advances through the text. The Internet Archive's online book reader is the best I've seen bar none, in particular its light-weight feel and auto-cropping of text so that the actual <i>content</i> of the book is centered on the page. I've submitted a request to evince (the GNOME PDF reader) that it do similarly. Still, I find myself constantly fighting with even the best PDF readers at finding the right balance between text sized large enough to read and fiddling with positioning the page onscreen.<p>Electronic formats may not be as good for first encounter and deep studying, but they are <i>immensely</i> useful for quick reference: the ability to 1) carry around a library of thousands of volumes and 2) instantly search to or open to a particular page or phrase is hugely useful. The ability to create an <i>external</i> reference that will find the relevant passage <i>in whatever form of the work you have handy</i> (similar to a URL, but not specific to a given instance) would be magical.<p>Some limitations of electronic formats can be mitigated somewhat: there are bookmarks, annotations, and other forms of marking up documents, though none match the immediacy of a penciled margin note, underlined passage, or dog-eared page.