Amazon's third-party ad platform got plenty of attention at Advertising Week, but the fact is that many retailers are now running similar experiments, says Jay Habegger, co-founder and of the OwnerIQ ad network. Best Buy and Wal-Mart both already repackage their website visitors for display-ad buys elsewhere on the Web. "A year ago, the effective media dollars deployed against audiences of other brands was effectively zero. ... Five years from now, it will be in the hundreds of millions of dollars," Habegger says.