Leave a book you love in a public place

The British newspaper The Guardian is running a book swap this week: http://www.guardian.co.uk/books/2011/sep/15/guardian-book-swap-15000-volume-giveaway. The idea is brilliant but simple, so you don't need to be in the UK to take part. Just leave a book you love in a park, street corner, bus, train, etc. with a note explaining why you love it. You can always crouch behind a tree in the park, street corner, etc. and wait for someone's paroxysms of joy and delight when they come across your book. However, this may lead to heartbreak if the stranger callously discards your book and/or note, so I wouldn't recommend this form of spying.

Effort involved: not much. You grab a book from your shelf, write a short note and drop it off. This is totally enjoyable effort, given that most people really like being literary (or musical, or cinematic, or whatever) evangelists.