Earlier quoted context omitted.
This only matters if your definition of efficient is along the axis of carring more books or minimizing space uptake. If your efficiency is based on the pleasure of holding pages, the visual aesthetic of multiple books, the maximum amount of time to go without a charge, collecting signed editions, etc. then eBooks are completely garbage.
They’re also superior in most ways as interfaces to works with more features than “main body text”, and to which you intend to refer again very often. Pop fic and pop non-fic, then, for ebooks. Excellent for those. Paper or both for most everything else.
My paper book library has increased every year; novels I want to own on paper (sometimes more than one copy), books received as gifts, technical books, art books, picture books, language books, reference books, mathematical text books, graphic novels (and indeed, some things that clearly are "comics"), a significant number of books that simply aren't available in electronic form (and I probably wouldn't want in electronic form anyway - if I'm buying a book from the 1800s I want the physical artifact!), more and more.
At the moment, the only benefit I see to the Sony Reader is that it's very lightweight and compact for a stack of 12 novels. That is a very serious benefit and it's a real lifesaver for travelling, but inside the house I'm paper all the way. The only problem I have with them is that I'm genuinely running out of space to put them. Every bookshelf is two (or even three deep) with books, and I've lost one desk entirely to books piled three to four feet deep. There is a real chance that I might end up finally giving up on renting purely to buy a house in which I can turn a couple of rooms into decent book storage.