I have one general rule for any e-mail that's mass forwarded: It's a lie.
I'm sure you get these every once in awhile. A friend forwards you an e-mail. When you scroll down to the bottom (because there are forwards upon forwards upon forwards of names and little >>>>>>'s down the left side), you find some dire warning or call to action. Maybe it's the worst virus ever. Maybe Bill Gates is going to give you $1000. Maybe Congress is going to pass a law outlawing toenails. In any case, it tells you to forward the e-mail to everyone in your address book (often with the line, "I'd rather get this twenty times than not at all").
It's a lie.
Something about e-mail leads people to believe anything sent is the truth. This tendency has been noted, leading to such things as the Gullibility Virus warning (I shouldn't have to tell you that this is a joke, but one never knows). And with Google and other search engines, it's very easy to check for real viruses. If Microsoft calls a virus "the worst yet," you can bet it will be mentioned on CNN.com, yahoo.com, or other news websites. It only takes a minute to check.
But, as a general rule, if you get a message that insists you forward it to all your friends, "It's a lie" is a good rule to follow.