Is posting a video on youtube s really good way to advertise?

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I have seen many videos on youtube which are purely meant for advertisement purpose. even youtube now allow tagging in a video so there appears arrows saying click here join us etc. also since youtube is a giant website I found that the page ranks of the video page is also high and thus they a get a free good quality back link. also youtube being busy with their large database never delete these type of videos. How do you find this type of advertising?