About 10 years ago, I read a short story written by Bruce Sterling, which gave me the original idea behind BookMooch. In the story, people wear a watch-like gadget which suggests small gifts they can do throughout the day, at very little cost to themselves.

You can read the story online, for free here: http://www.lightspeedmagazine.com/fiction/maneki-neko/

Nobody keeps track of how many favors they've given or received, because everyone benefits from the system keeping track of it for them, and from receiving these little favors all the time.

This was the philosophical foundation behind BookMooch : giving away books you no longer want is a small favor, but it's wonderful to receive books you do want.

The short story book that contains this story was originally published in 1999. Here is a short review of it:

"Maneki Neko" is an upbeat, funny story that portrays a logical extension of the late, lamented "gift economy" upon which the Internet was built. The central principle was that if people contributed what they could to the system for free, everyone would wind up better off.

Thanks to infiniteletters for finding this story online in the comments to Article in The Independent. It's been 10 years since I read the story, so hopefully my memory is not too far off about the plot.

Quickly scanning the story now, I came across this very-relevant dialog:

“Well, your network gift economy is undermining the lawful, government approved, regulated economy!” “Well,” Tsuyoshi said gently, “maybe my economy is better than your economy.” “Says who?” she scoffed. “Why would anyone think that?” “It’s better because we’re happier than you are. What’s wrong with acts of kindness? Everyone likes gifts. Midsummer gifts. New Years Day gifts. Year-end presents. Wedding presents. Everybody likes those.”

and the "smooch" feature was born from this idea.

thanks for BookMooch!