From a slashdot thread, I see a list of requirements for the next PDF replacement (whatever that will be):
– must require zooming in lots of times to be readable, until the page doesn’t fit on your screen
– must support two-column text, so you read down, up/across, and down again
– must behave differently near pagebreaks, so the scrollwheel suddenly skips 3 pages while the down-cursor stops responding
– should ideally make your browser crash or stop responding
– support DRM and ebook features, such as “being viewable only in a browser which displays adverts constantly”, “requires connecting to the internet for no good reason”, and “uses all your bandwidth downloading lists of people that it shouldn’t show the book to”