YouTube has always been very clear about the separation of editorial content and sponsored ads on its site: While the site is eager to sell advertising, placements as "featured" or "promoted" videos -- incredibly valuable, high-traffic spots on the homepage -- are not for sale.

The "featured" and "promoted" videos on the homepage are chosen by editorial criteria, and, in theory, are not influenced by who is spending money to advertise.

Or are they? Advertisers say that's not the case, and that "promoted" videos are routinely negotiated into advertising deals on the site. What's more, advertisers say YouTube uses the "promoted" video slots to help meet the ad impression guarantees it makes to advertisers who buy impressions on a cost-per-thousand views (CPM) basis.

A YouTube spokesman says the company won't comment on agreements with advertisers, but "purchasing placement on the homepage as a 'Promoted Video' is not a method of advertising we now offer."

That said, "promoted videos," featured at the top of the page, are rotated by algorithm from a pool of videos s