The usual traffic breakdown is very high anon traffic percentage. I just checked boingboing and for the last 30 days, 400k logged in pageviews vs 4.3m, anon so about 10%. whoops that was wrong, not sure where I was looking there 
Last 30 days all traffic, 4.7 million pageviews, of which 351,000 were logged in users. So 7.5% of traffic is logged in users.