Lawrence Lessig writes:
Theres an important distinction developing among user generated content sites the distinction between sites that permit true sharing and those that permit only what Ill call fake sharing.
A true sharing site doesnt try to exercise ultimate control over the content it serves. It permits, in other words, content to move as users choose.
A fake sharing site, by contrast, gives you tools to make seem as if theres sharing, but in fact, all the tools drive traffic and control back to a single site.
In this sense, YouTube is a fake sharing site, while Flickr, (parts of) Google, blip.tv, Revver and EyeSpot are true sharing sites.