I've received a recent flurry of Chain Letters, Petitions and Virus Warnings to my inbox. All these things are usually forwarded in good faith by unsuspecting computer users, quite often to all the people in their address book.
The first thing I do is check with Snopes.com to see if the e-mail I've received is known and, if it is on their site, read ALL the information on the page about it (just enter what the e-mail is about into their search box). You would be surprised with what turns up on there!
If it is known and shown to be false I usually hit the "Reply All" button, cut the forwardings and warning etc from the reply and, as my message, paste the Snopes page link with the note "Please read this" or similar. That gets sent to all the people that were sent the original by the person that sent it to me and also to the sender (that's what Reply All does). I then delete the message.
If it's a Virus Warning and it doesn't show up on Snopes I'll look at Sophos.com in their Hoaxes area to see if it's there (they also carry info on non-virus-related hoaxes, chain letters, scams and misunderstandings, their primary aim is viruses and hoax viruses though) again, using the search box. If it is I do the "Reply All" and give the Sophos link instead.
I've made it a bit easier to check on what viruses real and current and what the current hoaxes are by placing the Sophos powered top ten lists on the PC Help Index page.
Well, apart from needlessly worry people, expense (whole company networks have been shut down because of a hoax virus warning, losing the company time, business and money) and clogging up the e-mail servers (see: Pass it on Scams) the multi forwarded message can contain, literally, hundreds of e-mail addresses, which are a Godsend to a Spammer! (loads of lovely, working e-mail addresses to send the adverts for replica watches, pills, potions or links to sites of questionable material!).
So Please before forwarding on that latest e-mail to "Everybody You Know" check to see if it is genuine or a hoax / scam. If genuine then, by all means, pass it along. But if it's a hoax delete it and stop it in it's tracks!
If you recieve an e-mailed petition then look for the petition originators Web Site as a "proper" petition may well reside there, by all means, if you agree with the sentiments of the petition, sign it there and pass that link on if you feel strongly enough on the issue (often you will be asked for an e-mail address and have to click the link that is sent to you to confirm, this goes some way to combat fraudulent/multiple signings).