Yahoo! tends to be very secretive about visits, users and what not. When Flickr got taken over by Yahoo! there where many questions about how many users, terabytes of data… Here is some recent numbers that Flickr staff have mentioned
20 terabytes of data restored, after a storage glitch. It was not clear weather they moved all data to make sure there where no inconsisties, or just moved the data that had been lost.
4,000,000 users. Mentioned when users where complaining about there photos being used in large projects that made use of the Flickr API.
228,000,000 photos, with about 1,000,000 added per day
1300 Million page views per day, average, according to Alexa.