We know Google's (GOOG) YouTube is a tough sell for advertisers. But video site's sales team may be having an even tougher time than recent reports suggest.

YouTube sales manager Brian Cusack says YouTube is able to sell ads against "less than 3%" of the total videos on the site. That shaves more than a point off the 4% floated by the WSJ two weeks ago, which cited "one person familiar with the matter."

In comments to a ClickZ conference on online video in New York, Cusack said YouTube had been embraced by the movie studio and TV network advertisers, and was making progress with more conservative marketers in retail, consumer packaged goods and home improvement categories, which are overcoming the "perceived risk of what appearing next to user-generated content."

The biggest unknown: How many of the 4 billion or so YouTube videos watched each month actually carry ads. Presumably some of the most popular are also high-quality clips produced by partners, and those may have ads. On the other hand many of the viral hits on the site, such as last week's "Homemade Porn," run without advertising

Either way, it's a sign that while YouTube has a long way to go, or perhaps a testament to their abilities that they'll manage $200 million in 2008 revenue from such a small sliver of videos offered on the site.

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