AUUUGHGHGHH!!! Can't stand the danged things. I've got a filter set up in my e-mail to where if there's more than one FWD: in the subject line, into the trash it goes.
My guess is that e-mail is such a simpler method than snail mail that it naturally lends itself to abusive practices such as chain letters. I know of very few people other than extreme superstitious types who would take the time and trouble to copy a chain letter out longhand (or go to the Kinko's across town to make copies of it) and address 10 envelopes and use 10 stamps to send it to ten "friends" (aaak, with friends like that, who needs an enema?). Whereas, in e-mail, it takes next to nothing to add 10 people from one's address book (or memory) to the TO: or CC: field and fire off the e-mail in one shot.
The way to fight it?
A. Don't perpetuate it...break the chain. Refuse to forward the message, and delete it.
B. Write the person back and let them know how you feel about it. If it's a valued friend or family member, be kind about it, but be firm.
C. If it continues (from the same person), repeat B, but be less kind.
Eventually, hopefully, they'll get the picture. Remember, most messages like this emanate from someone you know.
Cheers,
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I know who you are...I saw what you did!