Interesting that my impression is more or less the opposite: I can read on a tablet all right, but leafing through is annoying and switching back and forth between three or four places in a big (thousand-page) reference book is so annoying as to be nearly impossible. The first, because rendering PDF pages (understandably) takes time, and the second, because I’ve seen no bookmarks interface as seamless and convenient as leaving a loose sheet of paper or even just your finger in the necessary place—they’re all fiddly.
I’d say there are two reasons from my reading from screens a lot: as far as the last couple of years go, if you know of a way to ship two bookcases or so from Moscow, Russia, to somewhere in the sane(r) world without spending prohibitive amounts of money (or having to return there in person), I’d very much appreciate it; before that, it’s not like ex-Soviet libraries stock any English-language technical or scientific literature issued after 1990, and paying the extra 50% for a two- to three-month-long Amazon delivery on top of the already-insane prices was hardly an option for a teenager or a college student.
I haven't found anything better than paper for technical docs, but getting a PDF and printing the few pages I need is amazing.
I think tablets are a decent secondary substitute for print-form only for publications like this with figures and images, and where the activity is more browsing rather than linear.
For general reading (eg fiction) I think print is optimal, followed by e-ink with normal tablets considerably down the list.
The ease of access to a library bumps up the utility of the ereader and tablet considerably.