As a poor starving college student, I love free stuff. Whether it's a free t-shirt, free food, or free books, if it's being given out I'm trying to get it. Making books available for free is a huge draw for readers, but it can also be beneficial to the author as well. even though they may might not make money off of the sales for the free book, if the book is at all decent it will attract readers to the author's other books, which he or she can charge for. The free book is an incentive to read more by that author, which will boost the author's ultimate revenue. I think that this type of gift economy can sustain itself because of the revenue created from people buying other products similar to the free one they received. People love free stuff; if the free stuff is good, it can lead them to buy the pricier stuff.