Mix media sharing are the words webdoc uses itself to describe its new microblogging service. And I am not sure if microblogging is the right term to describe it as it is rather the opposite to Twitter and other minimalistic sharing services. But the style of the site is the same to typical microblogging and social networking services by allowing following and the like.
Without a comparison it would be nearly impossible to describe webdoc. The posts at webdoc are rather complete microsites, which may include all kind of media, which reminds on other up to date internet technologies used in different or similar contexts like blogging services having a magazine layout or advertising technologies enabling to interact and sharing the content.
Having a look really is simplier. So below is an example of a post showing at the same time another way to share the posts by embedding it into a site. And here is the social network webdoc. (The page of this blog looks strange below the embedded element as all other content moved done. I guess this better should change after the Beta.)