PDFs look gorgeous on a hi-rez color screen; ebooks look dumbed-down. Compare a full-color calculus textbook or news magazine in PDF format vs. ebook format, and which would you rather have?

The problem is that US letter paper or A4 are both roughly 14" diagonal, and textbooks and magazines are often a bit larger, so you need something like a borderless 15" diagonal display with at least 300px/in resolution. I'm hoping that within a few years we'll see reasonably-priced tablets with displays like this and with serious battery life (say, 24 hours or so, because thinner isn't everyone's first priority).

"Compare a full-color calculus textbook or news magazine in PDF format vs. ebook format, and which would you rather have?"

The ebook format, because it doesn't make archaic assumptions about "paper size", and I can therefore read it on anything from a phone to a wall-sized projector screen.