Who Reads What? And What To Read?

This is something which only benefits from as many people using it as possible. Share Your OPML! takes a file that lists all of the RSS feeds to which you subscribe. Then it will tell you things like, “Which are the most popular?” and “Who subscribes to a particular feed?”
Not all RSS aggregators will save off a list of your feeds as an OPML file (sadly HotSheet does not, maybe somebody needs to add OPML import and export). But the main reader I use now since I’ve got Linux both at home and work is Liferea and it does. As a result you can see all my current subscriptions (you have to get an account on the site before that feature works).