I am interested in giving people ways to track their influence on others. Forwarding Tree's URL tracking is all about that: http://groups.google.com/group/forwarding-tree/browse_thread/thread/ad998b99b9e3b7a8

URL tracking allows you to see what happens to those URLs that you forward to others, post on your blog, submit to a social news site, etc. You can see how the URL propagates around the net in real-time.

In other contexts, one might show people their influence on wikipedia articles, search engine rankings, open source code, etc.