I have a friend who works in the big city and endures a long-ass commute by public transit every day. Each day he passes an informal honor library setup, a place where commuters can take and leave books for one another.
His hobby is to buy up works of subversive philosophy (according to his own lights) at used bookstores, which he then leaves at this honor library each day when he passes it. He reports that they are snapped up without fail.
When he told me about his hobby, I found it familiar. What he's doing is very akin to guerrilla gardening, only he's leaving meme bombs instead of throwing seed bombs. It's guerilla gardening, only with ideas.
I don't know if anybody here has the budget and inclination to leave permaculture books in places where strangers will pick them up and read them. But it's an amusing notion and I wanted to share it.