I like to give something with some personal touch, so I usually don't go for gift cards. In particular the more generic ones; at that point, just give the money (but I'm cynical like that).

As for books, tho:

I once went to a birthday party of an enthousiastic reader. He's comfortable with his own taste in books too, and doesn't like to veer outside of it. He likes books, it's a well-known fact about him; most people know what his favourite authors are.

So inevitably, when one of his favourite authors published a new book, he got five copies as a birthday present from five different people. (Edit: of which he had to keep one copy, and return four. So he had to choose which copy to keep and potentially offend someone, and ask the others politely for a receipt of a gift they thought was thoughtful)

I just gave him a book voucher. A book everyone knows you want, you'll get from everyone. I rather give something so you can get the book I don't know you want.