Lawrence Lessig on a key difference between YouTube and Flickr:
So there’s an important distinction developing among â€œuser generated contentâ€? sites â€” the distinction between sites that permit â€œtrue sharingâ€? and those that permit only what I’ll call â€œfake sharing.â€? A â€œtrue sharingâ€? site doesn’t try to exercise ultimate control over the content it serves. It permits, in other words, content to move as users choose. A â€œfake sharingâ€? site, by contrast, gives you tools to make seem as if there’s sharing, but in fact, all the tools drive traffic and control back to a single site.