RSS blogrolls are a federated social network:

As a starting place I manually identified twenty websites with OPML blogrolls. From these I can follow links to find 150 distinct websites. Several of the links go to YouTube pages, reminding us that RSS isn’t just for blogs.

The network is up to 1700 feeds. It’s already becoming obvious that there needs to be a way to search all of these feeds. It’s hard to find what you’re looking for in such a long list.