I had an idea for a plugin that I wanted to throw out.
On my site, I have a lot of contributors to a main blog. Everyone is writing and updating stories, articles and opinion pieces. A lot pictures are reused, but often by different people, necessitating them to upload the picture to their media library as well.
What would be awesome is if there was a way to create a media library that certain people would have access to. Everyone authorized could load images into that space and then embed any image or movie in that library into a post. As the administrator, I could upload images, graphics or clips and then have them available to anyone at the approved level to retrieve from the library. Anyone who wasn't part of the approved group wouldn't have access to the library, but would see the pics normally wherever they were embedded in a post or page.
Don't know what kind of wider interest there is in a plugin like this, but I do know of a bunch of people that run group blogs / newsites that run into similar situations.