Barnes & Noble may be close to giving up on looking for a buyer in a matter of weeks, five sources said Wednesday. Seven companies, including "strategic bidders" and private equity firms, have reportedly backed off after a recent round of bidding. Some of the unnamed companies told Bloomberg they backed off based on poor prospects for the Nook; they learned that it would take a long time to generate e-book cash and were jittery about competition with the iPad, Kindle, and Google Books.