The MIT Media Lab has created the concept of meme-mail, a way for readers of those frequently-forwarded pieces of “internet lore” we get in our inboxes so frequently to have accumulated anonymous data about who else has seen the message already. “We hope that by providing this information,
these messages will establish a stronger sense of their audience and community.” Here’s what the meme-mail FAQ, which is what the link above links to, answers the question, “Why are you supporting Internet chain letters? Aren’t these a waste of resources?”

We think frequently forwarded email has become an important grass roots way for individuals to circulate meaningful information to a wider audience.
Because messages are only forwarded widely when many people find them interesting, it actually employs a reasonably efficient, decentralized means of
resource allocation. MEMEmail enhances the decentralized nature of these messages by allowing people to get a sense of the messages’ audience. Previously,
this only happened when a centralized, mass medium like TV or a newspaper decided to report on the popularity of some piece of Internet lore.