From Amazon:
We are excited to announce Kindle book lending (http://www.amazon.com/kindle-lending). The Kindle Book Lending feature allows users to lend digital books they have purchased through the Kindle Store to their friends and family. Each book may be lent once for a duration of 14 days and will not be readable by the lender during the loan period.
All DTP titles are enrolled in lending by default. For titles in the 35% royalty option, you may choose to opt out of lending by deselecting the checkbox under "Kindle Book Lending," in the "Rights and Pricing" section of the title upload/edit process. You may not choose to opt out a title if it is included in the lending program of another sales or distribution channel. For more details, see section 5.2.2 of the Term and Conditions.
For more info on how Kindle Book Lending works, see our FAQ here: http://forums.digitaltextplatform.com/dtpforums/entry.jspa?externalID=581
