With those words, many a poster announced to the world that he too had fallen prey to one of the more annoying chain-mail, pyramid schemes plaguing the internet. I don't see the Dave Rhodes letter very much anymore, but plenty of other letters have filled the gap.
A pyramid scheme is basically a get rich scheme that might make a few people rich, but will just make most people poorer. Pyramid schemes are illegal, although prosecution is usually difficult. However, posting a pyramid scheme to the net is a good way to lose your internet access.
Pyramid schemes come in many forms. For example, many of the Saving and Loan failures in the United States were a form of pyramid scheme (enabled by the ill-adised deregulation of the Savings and Loan industry -- send your thanks to Ronald Reagan and Pat Nolan!).
Internet pyramid schemes/chain-mail have provided fruitful ground for parady. Enjoy!
Note: I don't know the original authors of all of these. If you see something you wrote in here, let me know and I'll give you credit (or remove it if you prefer).
Also, if you have any other such parodies, send them to me and I'll add them.