YouTube has been hitting all sorts of milestone marks over the past few months, with 1 billion subscriptions, over 2 billion daily views, and over 24 hours of video uploaded each minute. Yesterday, the video giant reached another milestone when promoted videos hit half a billion views.

Promoted videos are featured on the site, for a price, next to relevant search results. You’ve probably noticed them on the right side of the screen when you’ve searched for videos on YouTube, as well as highlighted throughout your search results, but you may not know how these promotional video campaigns work. Basically, advertisers choose a video that they’d like YouTube to promote, provide YouTube with promotional text and let YouTube know which keywords they would like to trigger their promotion. When someone clicks to watch the video, the advertiser or video creator pays YouTube a set amount. Advertisers only pay when viewers click. However, with 500 million promoted video views in not quite two years, that’s a lot of revenue!

YouTube writes about the growth of their promotional video program on the company blog. They write that since the Promoted Videos ad format was announced, nearly two years ago, “thousands and thousands of advertisers have taken advantage of this ad format to entice likely customers with videos about everything from smoked brisket recipes to magnetic jewelry to sneakers. Politicians and political activists have used Promoted Videos to argue for a proposition or against an issue. And large companies have reached wide audiences with movie trailers, recipes, and ideas for Halloween.”

YouTube also announced that in the last year they have seen a 6-fold increase in viewers clicking to watch Promoted Videos, which is pretty astonishing. Perhaps YouTube viewers don’t realize that promoted videos are glorified advertisements, or maybe advertisers are just getting so good at producing entertaining, quality web videos that viewers are excited to click and see what’s being promoted.

Advertisers who are thinking about getting into the business of promoted videos on YouTube will have it a lot easier than when the ad format was first announced. Recently YouTube has expanded Promoted Video ad campaigns from the United States to twenty different countries, made a video targeting tool available for Promoted Videos and given advertisers the opportunity to use Promoted Videos to manage campaigns across multiple clients with AdWords.

If you are an advertiser, have you run Promoted Video campaigns with YouTube? If you are a viewer, to you click to watch Promoted Videos?