Google and Yahoo sponsored link impressions (including sites in their search and contextual advertising networks) increased 16 percent from August 2005 to January 2006, with Google serving nearly twice as many impressions as Yahoo, but Yahoo growing at faster rate, writes ClickZ, citing Nielsen/NetRatings data. Google delivered 41.1 billion sponsored links in January, 14 percent more than six months ago; Yahoo served 23.2 billion, 21 percent more during the same period. "Yahoo is moving more quickly is because it's growing off a smaller base," according to Nielsen/NetRatings chief analyst Ken Cassar.

"E-commerce companies have always been the biggest users of search, and I suspect that that will be the case indefinitely," Cassar is quoted by MediaPost as saying. "We will start to see brand advertisers using search increasingly as they become more comfortable with the internet and their tactics evolve."

eBay accounted for the largest share of sponsored search ads on both Google and Yahoo, having purchased some 2 percent of search inventory on both. eBay's Shopping.com was the second-largest advertiser on both. On Google, Local.com, Target, and Expedia.com ranked third through fifth; on Yahoo, the next three were University of Phoenix, LendingTree.com and Target.