I did the Book swap thing this week (see I LOVE THIS: The Guardian and Observer Book Swap).
I left a copy of ‘Birdsong’ on the Victoria Line, sitting on the seat next to me. It was avoided by Members Of The General Public all the way to Green Park. Then this lovely lady picked it up and placed it in her lap for a few stops, and, upon arriving at Euston, seemed to suddenly happen upon it, as if by surprise. It was a nice moment: me, viewing her reaction to my little gift in the reflection of the windows opposite.