Flickr is yet another social networking system. It allows you to upload images to be viewed by people in your network, as well as integrate IM and group chat functionality. Microsoft's Three Degrees system has similar features, at least for sharing images and playlists with groups.

It seems like there's two components to this, one is the multimedia aspect - pictures, playlists, IM, chat, and the other is the use of the social networks as a content/information delivery conduit. In order to have this sort of functionality work, you'd want to partition your networks into smaller networks that could be access controlled differently. But maybe that'd actually be interesting, being able to route information to people in various subnetworks. I bet you could bolt something like this into Groove, if it's not already there (I haven't kept up on the status of Groove). Of course you can imagine all kinds of good Web Services stuff happening inside of the content routing network.

The other interesting thing about Flickr is that the client side app appears to be written entirely in Flash.