Starbucks has partnered with iTunes to give away free content since 2007, offering free redemption codes for a "song of the week". Earlier this year, Starbucks began offering a "Pick of the Week" iPhone app, including a high-profile promotion of SPY Mouse, a new game from Firemint/EA Games.
This week, Starbucks is offering an iBookstore redemption code for The Night Circus, a $12.99 book from Erin Morgenstern. The book is also being heavily promoted on the front page of the iBookstore.
Update: The "free" book does indeed appear to be an extended sample, not the complete book.
Starbucks noted last month that it would begin offering free "Pick of the Week" redemption codes for "Apps, extended samples of books on the iBookstore, TV shows, and more from iTunes."