It's been called a stunt, a desperate move, and "little more than a gimmick." It's been derided as a failed idea already tried by Amazon's A9, iWon, and other rebate-hawking sites that never gained traction. It is, of course, Microsoft's Live Search Cash Back, the first of what promises to be a series of "disruptive" initiatives designed to derail Google's overwhelming, yet ever-growing dominance in search (now consisting of about 62% of all U.S. searches, according to comScore).