Back when I was at NewsGator, we wanted to know a bit about how people used the client RSS apps (Inbox, FeedDemon, and NetNewsWire). As I recall, we did almost nothing in the way of compiling data — possibly in part because I dragged my heels on it.
But we did learn one thing that I happen to remember: the average number of feeds for a NetNewsWire user (who also used syncing) was 26 feeds.
I had figured it would be around 75. Nope!