YouTube “is a popular free video sharing website - founded in Febraury 2005 - which lets users upload, view, and share video clips Unregistered users can watch most videos on the site while registered users have the ability to upload an unlimited number of videos. Related videos, determined by the title and tags, appear to the right of the video” (from Wikipedia).
As for those who study languages, as we are, it is interesting because you esily find videos which describe the different cultures you’re interested in and you can listen to native speakers who talk about the most different topics as well. But I think that the most important possibility to be exploited by these kind of visitors of YouTube is that of keeping in touch with the various aspects of nations and people.
If you have some time to spend in the net, it is probably one of the websites which offers you the largest range of material to explore! Have fun!