Here's a question I posted to the Drupal.org forums at http://drupal.org/node/183302 . I'd love to see an answer, so will ask it to Drupalace.com readers as well:

I am creating a new site whose topic will encourage readers to "share" specific pages' content with other people, by means such as:

* forwarding the page content to others
* pasting the page content into email (or into other sites' forums, comments, etc.)
* pasting the page URL into email (or into other sites' forums, comments, etc.)