I had a discussion with a client the other day. We had already built them a website, and designed a set of integrated, cross-pollenating autoresponder series to offer different whitepapers to his visitors. (Cross-Pollenating means that when someone joins one autoresponder series, they'll eventually get a promotion to the other autoresponder series. They all promote the others.)
They spent a considerable amount of time and money developing the whitepapers that are given away in the series, and the subsequent autoresponder messages that dive deeper into the points made in the white papers. It's really an excellent piece of marketing.
The goal of the autoresponders is to