I studied mathematics in the 80's, a lot of my peers read the library copies routinely, either systematically from cover to cover, for specific reference, or for fun (flip open at random, see what you get) - maths people love maths books and TAOCP is very much a maths book - since then I've rarely met anyone with am actual volume set that seems to have any idea of the contents.

The Dragon book I still own, a paperbound version that's as dog eared as a book can get and still hang together as it was the reference for three of us working on a few compilers of our own back in the day.

The C Book I no longer have despite having bought four to five copies :( That book's never been much of a boomerang.

I worked at one of the national labs and the books I'd see on shelves were usually ones from when folks were still students. The pristine unread books were either bound copies of the person's dissertation, or books he authored.