Google doesn't need to partner with Yahoo to eat away at Yahoo's market share in search. That's what YouTube is for.

In August, YouTube became the second most popular search engine, essentially bumping Yahoo into third place. And now Google is introducing search ads to the site.

Ads for Oliver Stone's new movie "W.,"the University of Phoenix, Simple Shoes, and Home Depot now appear alongside certain search terms. Says AdAge:

"If the targeting in that example seems less than relevant, it's because the pool of advertisers is small as YouTube beta tests the format. Ad

Age has also heard quality controls are under development to bring the format more in line with Google's regular search ads, in which placement is a combination of quality score and bid price."

YouTube received almost 2.6 billion searches in August, compared to Yahoo's 2.4 billion, according to ComScore. Video searches are not as easily commoditized as text searches — viewers are often looking for entertainment and information more than purchases — so YouTube search ads aren't likely to generate as much money as Google's AdWords, but that sounds like cold comfort for a company like Yahoo.