The very clever Gary Vaynerchuk
implemented on the website for his new book, The Thank You Economy
(due for release March 8, 2011) a slick little marketing trick to allow people to read more.
At the top of the book's website, you can download a good chunk of chapter 1 for free. To "unlock" an additional chapter, you have to tweet about the book. Bingo! You get what you want—free content—and he gets free marketing for his book.
Now, I'm not the most prolific tweeter, nor do I have the largest of followings, but still, my measly 120 followers (all of whom I sincerely appreciate, by the way) have tens of thousands of followers between them, so even if only a handful click the link and then tweet to get chapter 10, it's unquestionably a huge ROI on whatever minuscule cost was involved with setting it up the unlocking of the pdf via Twitter.
Maybe he's not the first to do this, but it's a bloody brilliant strategy, and is, for all intents and purposes, free.