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.
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 much too fiddly.
I haven't found anything better than paper for technical docs, but getting a PDF and printing the few pages I need is amazing.