I had seen a project like this mentioned over at hula seventy though I'm not sure if her project of leaving affirming little notes around was spawned by Hope Revolution or not. Here's the story:
A woman in Manhattan started the Hope Revolution web site and project, advocating that we join her in generating small, positive little notes and leaving them in places where other people -- strangers -- will find them. Stumbling across this idea again yesterday, I was ready to act.
I made my first set of notes (see below) and yesterday started leaving them places. On the table after we finished eating our Chinese lunch, in the children's section of a local bookstore. The very top photo shows a note propped up against the Heart Stones book; after taking the picture I decided to tuck the note IN the book instead, hoping that the ultimate owner would find it (and preventing a store employee from just tossing it).
There's a flickr group if you'd like to see more.