It seems that Google has done a good job cornering the online ad market and the question is where rival Yahoo has been the whole time. Part of the answer may lie in their announcement of SmartAds - a new crop of display advertising that aims to serve up display advertisements based on a user's age, sex, Web surfing habits, shopping habits or location all on the spot, in real time.

For example, a user visits a travel-oriented site: an ad appears with travel destinations that match previous Web searches (that website you visited exploring Tahiti) and destinations (that trip you booked online to see Aunt Sally last week), and the fares all originate from your nearest airport.

According to eMarketer, the targeted ad market is expected to reach $1 billion in 2008 and $3.8 billion by 2011.

Todd Teresi, Yahoo's senior vice president of display marketplaces said that the goal is for "consumers to view advertising to be as relevant as the content they're looking at."

Yahoo will begin rolling out SmartAds with travel-related clients before extending to different markets by the end of the year.