I've got some on my own shelves of course, but the break room is full of them. People must be doing spring cleaning or something. Most cover old versions of technologies I never really cared about anyway, but I hate to see them just lying there, or imagine them taking up space in a landfill. Would libraries take them, or can they be recycled? Or maybe Martha Stewart has advice about turning them into Christmas ornaments, or mixing them with truffle oil to make delicious hors d'oeuvres?
Where I live, the public library doesn't take computer books because they "can't tell if they are current." Really? When the copyright is the current year and you have that title on your shelf, you can't comment on it? The local university library has a better system. They take anything that isn't obviously falling apart and do one of three things - circulate it, use it for the book sale or toss it.
Those aren't really old books though. That's what I do when I get a .NET book or other book I know I'll never touch again from a publisher for review. Old books I keep until they are obsolete and then recycle them.
We do have a number of obsolete books in the printer room. Someone had the idea to start a "library" but most of this library is things that should have been tossed. And now since they aren't really owned by anyone, nobody really has the responsibility of tossing them. Whereas I keep my library (of not obsolete books) in my cube with some at home.
I do have a FEW obsolete books at home for sentimental reasons like the first Head First book I've ever owned.
I like paper books better than electronic books so this problem isn't going away for me.
If they're in decent condition i.e. not crumpled and no writing all over them (OK, I admit that's a long shot for any useful computer books...), you may be able to sell them to Amazon via their "Trade-in" store. I cleared a load of books off my shelves recently and managed to sell quite a few like this (about GBP100 worth). You enter the book details via an online form and they generate a price. If you like the prices quoted, you can then generate a packing slip which lists your books and prices, and a mail slip to stick on the parcel. Then you mail your parcel off to their intermediaries, and a week or so alter you get an Amazon voucher for the specified amount. Here in the UK the postage is free - not sure about other countries.