My friend put me on to this site: www.akoha.com;

In a nutshell, you purchase a set of cards (for a very small price) that contain various 'acts of kindness'; each time you do one, you hand over a card which has a serial # on it - the recipient enters the serial # on the website and then 'plays the card' on someone else....you can then track the journey of each good deed via the site.

Besides being a sweet idea and a novelty, what  I REALLY like about it is it gives you a 'prop' to kickstart interaction...I'm all for this idea of nurturing 'community' but it can often be plain shyness that stops adult strangers making contact - and a prop can help :)