Have a look at this Search Engine Results Page: http://www.google.com/search?q=kenyan+music Kenyan music is a pretty high volume search. Check the backlinks for kenyangospel.com This site ranks top 5 and you will find that majority of it's backlinks are from YouTube music videos. It has no links with the anchor text 'Kenyan music'. Most of it's dofollow backlinks are either with the anchor text 'Kenyan gospel' or they are image links. This means we have a site is ranking highly for a high search volume competitive term on the back of old YouTube links in the 'music' category. Does this point to YouTube links having some value at least regards passing authority?
Even Wikipedia links are nofollow, but it's widely accepted that they still influence Google in measuring a site's authority. Nofollow links, though the bot doesn't divert through those links, they are still crawled, so can still influence rankings in a small way. However, in this case study, we are seeing a site achieving very high rankings for a chunk of YouTube links