I've been fiddling with tracking registered vs. guest users, specifically the number of pages that are served to each group. It turns out that guest users account for solidly 1/3rd of our overall number of served pages. That's much more than I could have guessed.
For what it's worth, those statistics could be skewed by registered users who are not logged in, and thus appear as guests.
The question, though, is who the heck are all these people? We're talking thousands and thousands of pages per day.