Yeah, I have a lot of paper books that aren't available digitally yet (or are available digitally but in incredibly badly proofread copies I'd have to put hours of work into, or are available digitally but I'm not willing to give up a paper copy). Still, I could condense the shelves a fair bit by just replacing Elizabeth Moon, Terry Pratchett, and a few other authors with digital copies, and I expect some of my nonfiction collection is available as reasonable ebooks. (OTOH, there's also the money factor: I already OWN the paper books).

But that's also a big reason I haven't fully switched over as many people have--so many of my favorites just aren't available digitally.