Bring your nook or mobile device loaded with their Reader app into any Barnes and Noble store, show it to a store associate, and you'll receive a promo code that entitles you to download a free ebook from bestselling authors. Nice. You'll get a different book each week and the first is Alexander McCall Smith's "The No. 1 Ladies' Detective Agency", which will be available through this week through May 23. Next week's book will be Jim Butcher's Storm Front.
Once you get the promo code, you can use that code to download the book for free by entering the access code at bn.com/redeem . You can read the book on your nook, computer, iPhone or BlackBerry running the B&N Reader app.
Here's the info from B&N.