My current project is a fairly interesting CCK based site with a lot of node referencing going on. It's core is basically a normalized structure of three different node types. (books, authors, and publishers) All content produced on the website is relevant to one of those three things.
I've somehow found some amazing people who are interested in helping my with my image/file manipulation work for Drupal. Based on concepts that have been brewing in imagecache (dynamic image generation and manipulation, automated derivative generation, image processing automation) I've started an endeavor to break this stuff into usable discreet chunks.
It may be interesting in drupal to have a cck node type of content-folder, then either use a filefield on the 'content-folder' node or a nodereference with a link to a 'content-file' with a filefield. You could create file hierarchies / file management workflows....
Today, I got imagefield pretty happy I think. The outstanding ui bugs from the switch to using content.module to store the fid are closed. The views integration works properly, at least for single imagefields...
There are lots of really cool social networking applications out there. Each is unique in its marketing, but central in what it does. Host an online persona, allow members to associate & 'link' to each other, allow people to search for site members.