Read a good book. Register it at BookCrossing. Label the book with its BookCrossing registration number and a short note about BookCrossing. Release it for someone else to read (give it to a friend, leave it on a park bench, donate it to charity, “forget” it in a coffee shop, etc.) and be notified by email each time someone records a journal entry for that book on BookCrossing.
The very first book I released was picked up the next day and is now heading for Alaska.
[The BookCrossing website takes pains to reassure publishers and authors that this system will not discourage people from buying new books. Some BookCrossing enthusiasts, they claim, actually buy two copies of every book, so that they can set one free and keep the other. BookCrossing claims almost 3 million members and half-a-million books registered. --CP]