For a history and explanation on chain letters (the ones asking you to send it for others), visit here:

http://www.snopes.com/luck/chain.asp

Some chain letters claim "you can receive rewards from companies by simply forwarding an e-mail message to your friends". This is a common hoax too. Read here for more info:

http://www.snopes.com/inboxer/nothing/billgate.asp

Many "dying child" hoaxes circulate online, each of them asserting every forward of their supplications will result in benefactors (either named charities or corporations or unnamed millionaires) directing set sums towards the care of the stricken youngsters. While these lack the specificity of "Send this to four people" instructions (they instead direct recipients to "Forward this to everyone you know"), the languishing children are imaginary, and the forwarders add nothing of themselves to the mix (neither prayers nor donations), they are a close enough fit with the altruistic class of chain letters to be considered
a legitimate variant.

http://www.snopes.com/inboxer/medical/cancer.asp

First and foremost, e-mail tracking programs do not exist. That folks continue to fall for myriad varieties of these leg-pulls is in part attributable to netizens having caught so many references to these non-existent programs that the new hoax is able to continue building on an already partially-constructed platform of belief.

(As with every other technological issue, the statement "e-mail tracking programs do not exist" becomes less and less true every day. It is possible in some cases to determine who has read a particular mail message, but there is no method of doing so that will work with all the myriad of e-mail programs out there or keep track of who forwarded the message to whom.)