I'd like to be in the acknowledgments of many people's books. Not just to see my name there, but to remember having helped someone. Sometimes it will just be thanks to an anonymous reviewer. It would be nice to think of peer review as giving assistance to the author, rather than merely exhausting gatekeeping.
I don't remember anyone leaving me out of an acknowledgments page. People are good about this, generally. If someone doesn't thank anyone, I get suspicious. Either they never talk about their ideas with anyone, or they are ungrateful. Writing is a solitary activity, but it takes place in the context of intellectual exchange, what Creeley called the "company."