Don't get me wrong: I always enjoyed reading at core, both fiction and non-fiction. But the zettelkasten completely changed the way I read non-fiction. Before I had a zettelkasten, I felt pressured to reduce my pile of unread books and to get through everything as soon as possible. The amount of topics that interest me is large, and so is my pile of books, but time is little.
I noticed, however, that I would oftentimes not remember much about what I had read only two weeks after the fact, and therefore the actual learning curve was rather low, the time spent reading seemed more or less wasted except for the sense of gratification for having read X amount of books in the past weeks. Reading was more about improving my statistics on how many books I had read and how much time I spend on a book instead of on what I actually learned from it. After every other page turning, I used to check the page number and somewhat wish it would increase faster. Probably I am not the only one here who felt this way (or am I? That is kind of my question and my reason for starting this thread). It is not that reading was a tiresome activity to me, else I would not have done it in about 50% of my free time. But it felt, to a degree, like an obligation.

This totally changed with the zettelkasten. With the zettelkasten, this sense of obligation, of having to finish so many books as soon as possible, vanishes entirely. There still IS a huge pile of books (or actually, several piles) in my room, but the reading itself becomes more of a quest instead of an obligation. It becomes a quest for interesting ideas and thoughts that I can extrapolate from the author's thoughts. When in the past I notice the page numbers increasing from 24 to 27, 30, 32,37,41 etc., now I almost forget that I am progressing in the book only to find myself on page 41 already in the first reading session after about an hour, with often at least five slip notes inserted between page 1 and 41. I still get through books about as quickly as I used to before, although putting everything into the zettelkasten later on does of course consume some time - that's what Luhmann already experienced himself when he said that most of his time is spent not writing books but working on his zettelkasten. But reading itself, being the foundation of the zettelkasten, becomes more of a pleasant pastime instead of a duty when you use the zettelkasten.