Once you receive a chain e-mail, you are likely to be receiving a lot of extra junk mail soon thereafter. Although people sending these e-mails have good intentions, they are unwittingly subjecting your e-mail address to being sold over and over again to the spamming industry.
A chain e-mail can be any e-mail that is likely to be forwarded, such as the typical "pass this along" type or the rather insulting "pass this along or else..." type. The e-mail addresses on virtually all of these e-mails eventually get "harvested" by automated programs looking for active e-mail addresses. The harvested addresses are then sold to any and every spammer looking to make a few bucks and all you get out of it is at least two years additional of junk mail.
Even though by the time you get one of these your address is already doomed, you had better nip it in the bud and tell whomever sent it to stop doing it. The most polite way to ask them to stop would probably be to reply with an article, such as this one (hint! hint!).
If there indeed is information you would like to pass along to friends and family, you can usually protect the recipients by using the "blind carbon copy" technique. First, delete any e-mail addresses from the body of the e-mail. Or, if you are feeling especially thoughtful, you could take the time to copy only the information you want to share and paste it into a new e-mail. Then, for the primary recipient (the person in the "To..." field), put your own e-mail address or a completely bogus one; for example, Nobody@nowhere.com or MyFriends@TheirEmail.com. Lastly, put the actual recipients into a field called the "blind carbon copy" (or BCC) field.
Much of the e-mail software commonly used, including web-based e-mail software, hide the BCC field by default. But this field can usually be easily shown. For example, while composing an outgoing e-mail message using Microsoft Outlook, click "View" on the menu bar and then click "Bcc Field". Instructions for a majority of the others are at http://rrudder.com/safe/bcc.html.
Note: ironically, some e-mail service providers flag as spam and remove messages for recipients that appear only in the BCC field.