There are many aspects of a library of technical books that I miss online: the curation process, the higher bit rate once you are holding the book, and the lack of distractions in the library.
What I fear may go away is the long form books offer. When exploring a new topic, articles are often too dense. In books, authors can establish the background, help create a shared vocabulary, and motivate what is often so condensed in a research article.
There was just recently discussion about books on HN. It was based on some blog post where the author complained about the book format and how hard it is to remember what you just read.
The discussion revealed that people don't learn in shool how to read and study with books anymore. Of course you don't remember much if you read the book from start to end. E-readers may share the blame. It's very hard and slow to study with e-book. If you spend hours studyin, you really need a book written into a paper.
Books are damn good interfaces for reading long-form text. Footnotes, end notes, indices (sure search is handy—indices are better for some things, though, by excluding invalid partial matches and other irrelevancies) glossaries, integrated author bios and expert introductions, and so on. Multi-page marking with near-instant switching. Two pages visible at a time. Cover, title, and author visible when sitting on the table not actively in use, to help passively absorb and retain that info—ever forget who wrote an ebook while reading it? Spatial recall. Margins to mark on or write notes in. They're excellent. E-book readers are a replacement only for disposable cotton-candy fiction—which has its place, and that part's nice.
Maybe one day computers and digital readers will actually be good enough to replace books. They're not even close today. The tech's just great.
For example, I use Foxit for looking at PDFs. Maddeningly, I cannot view two PDFs at the same time in different windows. There is no technical reason for this limitation, in fact, the limitation was deliberately programmed into it.
I'm pretty sure the people who program PDF readers have never actually used them. (There are a number of bizarre and trivial limitations to them that are trivially fixed. For example, many readers can only remember the last page read for the most recently read PDF. So if you open another PDF, your earlier place vanishes.)
For me, it's only partially a technical problem. If I need to really study something, I always print it out or buy the book. Honestly, I don't really understand why, but I'd guess that my comprehension and patience are at least double when reading a hardcopy.
Another advantage for me of physical books (etc) is that you have something like "tactile memory." What I mean by this is that very often, I can find where something was mentioned basically by how the book feels when its opened (e.g., how thick the pages are in each hand). A similar thing happens with shelves of books.
This is pretty hard to replicate with better tech.
The technical problems are largely trivial, and yet in over a quarter century's use of PDFs, mass-market readers fail to incorporate them. One might begin to suspect an incentives alignment failure within the industry.
I use a (reasonably good) Android reader which affords metadata presentation and editing, but lacks an "author" field.
None of the issues I report ever get fixed, either. I don't bother reporting them anymore. I just complain on HN :-)
I remember on PDF reader on a tablet which would remember your last read position only in the last 3 PDFs you opened. Open another one, and one gets pushed off the bed. I simply cannot understand the train of thought that concluded that 3 was the lucky number here.
It's funny, as someone who grew up with books and the burgeoning world wide web, I hadn't thought of this. When I'm learning a topic I tend to buy or print books so I can soak it in. When I to learn a quick task I go online. Books tend to be great for the why's of something but not the how's. Online is great for the how's but not the why's. I think a blended approach has ended up being the best way for me to learn. I do have a genuine love of books though.
What I fear may go away is the long form books offer. When exploring a new topic, articles are often too dense. In books, authors can establish the background, help create a shared vocabulary, and motivate what is often so condensed in a research article.