I have several chain letters which serve as extreme examples of what can go wrong when people just continue forwarding the original message over and over. To see some, go to my chain letter page and search for the text "a long list of headers remains attached". If you found this page by following the "removal" link from one of those pages, I'll be happy to remove your name/email. Just let me know the URL of the chain letter on which you found yourself and send me an email at firstname.lastname@example.org.
The reason I don't remove all those surplus headers immediately is that those chain letters serve as great examples of email forwarding abuse and tie into another pet cause of mine, the use of bcc to protect your correspondents' email privacy. Since those pages are quite popular, several people have been surprised to Google themselves and find one of the top links entitled "With Sex All Things Are Possible." So think twice before forwarding lots of email addresses (as well as your own) about where they might end up. You lose control of an email the moment you hit Send.