Ning - Create your own Social Websites!: "Ning is the fast and free way to create custom Social Websites!" Yes, that's their tagline. Indeed, after trying it myself, I find it very handy especially for beginer. You can copy all sort of socialy networking site, for example, video, photo and group site and make it your own. The registration is simple and handy. No hassle what so ever.
Other notable functions is the ability to mashup photo and video with maps and soo on. Although, I think the limited ability to customize the your site's look with a simple template editor (which Blogger have, for example) was it biggest letdown. User might find it troublesom to change it, especially those who do not understand programming.
Read what Techcrunch, Mashable and O'Reilly think about Ning.