Last year Devilman started to leave books that he had finished reading on the El for others to find, hopefully read, and pass on. A stealthy way to encourage reading, plus give a book a second chance at a reader, rather than spending the rest of its life languishing on a book shelf.
Now, according to the NY Times, I see that once again he is an early adopter; whereas Devilman was just doing his book drops with no thought of tracking, members of Bookcrossing register their books before letting them go, and then hope that whoever picks the book up will notice the registration number, and check into the website with their wheres/whens of their findings.
It's a cool idea; even if no one ever acknowledges finding the book, there's always the hope that whoever finds the book will read it and appreciate it. Of course, in today's security paranoid age, you might want to be careful of where you drop your book; it would defeat the purpose if the copy of The Shining ended up triggering a bomb disposal unit. But some things are worth the risk.
The closest I've ever come to giving a book to a stranger was back when I lived in Yerba Buena. I was riding the N-Judah one day, while reading a copy of A Rebours. A kid got on, looked about maybe 16-17 years old. He had long hair, a battered leather messenger bag and was wearing a 1950s suit and a tie. In a sea of track suits and hoodies; he stood out--definitely he was going Against the Grain. I had seen him a couple of times before, and he was always dressed the same. When the street car got to my stop, I shoved the book at him saying: "You should read this." He took it and I jumped off. I have no idea what he thought; probably that I was crazy--but I hope he read the book...I never saw him on the street car again...So that's not quite the same thing as Bookcrossing, but still, my attempt to do my small part in introducing young minds to the decadent movement and Gustave Moreau.
I have sometimes been tempted to sneak small press books onto the shelves of commodity bookstores but never had the nerve to try.