Multiply (multiply.com/m/) is a social networking site which claims 6 million members. Multiply's mobile edition comes in two forms, one for the iPhone and the other for all other mobile devices. The two share the same url with browser detection serving enhanced Ajaxized content to iPhones.
Multiply is a relatively closed network. Without a Multiply account you can't do anything on the site. You can register right on the mobile site or on the Multiply desktop site at multipy.com. Registration requires only an email address.
Multiply's main focus is content creation and sharing. Users can have a blog. The blog posts and comments along with whatever sharable content (videos, images, games) the user has uploaded are the focus of a Multiply home page. Comments appear immediately giving the site a bit of a chat like feel. Everything you publish can public, private, shared with only your contacts or shared with your network which is your contacts plus everyone they are connected to through the contacts chain.
The Multiply Mobile is generally well designed except for the photo album pages which can contain over 100 images per page. The images are small, 120x120 px, but small images add up. I saw one page with 133 images that was 600 KB! in size. This is on the regular mobile site not the iPhone variant and is much too big to load on most handsets.