It's hit-and-miss, though. I see no rhyme and reason in which books they're interested in, and the prices.
Just the day before yesterday I took some cooking books in pristine condition to the library. They used to have a book-swapping box outside. It was gone.
I went in (not too thrilled with the prospect of lugging it all back home) and asked about it. No, they don't have it anymore. I can put my books in the "free section" inside.
I did that, the librarian walked by to take a look and snatched the books away. "They are good, I'll see whether we can use them for the library. Usually we only get books we throw away immediately."
By "getting ride of it" I assume you put it into a glass case on your office wall. I admit it does deserve such a place of pride.
I don't think this is a good benchmark at all. It's a natural human tendency to think that we each are representative of "most people", but that's very often not actually true.
I prefer to donate unwanted books to the library, thrift shop, or used book store. Those organizations are in a better place to judge what most people want and what they don't.
Lisp in Small Pieces. Sure, here on HN many people would be interested in it. In a smallish town, even though there's a technical branch of a nearby university? Forget about it.
English books? The library isn't interested (for good reason, they have limited shelf-space and very little demand for English books, there are two shelfs of English fiction and that's it).
And even university libraries. I once asked them to buy Compiling with Continuations by Apple. A real classic. No, they won't. Too old, they won't spend money on that. Especially since it's available in several libraries throughout Germany. I am certain they would have zero interest in most of the computer science and programming books on my shelf.
Through it, you can borrow books from any library that is part of the system, which is almost all of them -- so even very specialized or obscure books that your local library won't carry can be ordered through them for borrowing.
Carnegie Mellon teaches a compiler course using continuations so I'm not sure what's "old" about it.