Well, almost never. I had a pile of detective novels in Russian that my ex-wife left when I got divorced back in 2002 that I tried to give away, in vain, and finally tossed into the recycling dumpster for paper.
I keep all books. I may box some up (I use plastic sealed boxes instead of cardboard book boxes) and I may eventually give away some of those boxed books to friends or relatives who are interested in them, but I don't throw them away.
With children's books, I am also now reading them to my children. I have to say that I am not sure what sort of book is so simple that it duplicates a wikipedia article, but I would generally advocate boxing up unused books and keeping them somewhere if possible.
ἡ δὲ κἀκ τριῶν τρυπημάτων ἐργαζομένη ἐνεκάλει τῇ φύσει, δυσφορουμένη, ὅτι δὴ μὴ καὶ τοὺς τιτθοὺς αὐτῇ εὐρύτερον ἢ νῦν εἰσι τρυπώη, ὅπως καὶ ἄλλην ἐνταῦθα μίξιν ἐπιτεχνᾶσθαι δυνατὴ εἴη. – Procopius
Ummaka qinnassa nīk!
*MySmiley*