Around 6 months ago, I was looking in to promoting my dreamhost affiliate link to a popular website/newsletter. Dreamhost allows you to create promotional discount codes which give your user a discount of up to $97 - and you keep the remainder. This can be applied to any Dreamhost bill you have, or paid out by Paypal.

I set up a code that was the name of the site in question (so for this site you would type in "osworld"). The discount was $50, so I would get $47 for everyone who signed up using it.

The discount code was never promoted, due mainly to the price for the advert being a little high, and nobody ever knew it existed.

I've just looked at my Dreamhost affiliate stats, and someone has signed up using my secret promo code, getting me a nice $47 for 2 minutes work setting it up. The only explanation I can think of is that they took a random guess at a code and got lucky.

Dreamhost (aff)