After climbing steadily in search queries over the last 12 months, Ultrabooks as a term is just about passing the threshold into true mainstream consumer territory. The launch of Windows 8 and a number of eye-catching convertible Ultrabooks look to be helping in a big way. The latest evidence comes to us in the form of a new Ultrabook ad from Best Buy, the largest consumer electronics retailer in the U.S. The retailer is also offering a $100 discount on an Ultrabook when you turn in a working laptop.