Fost interviews Flickr chief Stewart Butterfield as well as Delicious' Joshua Schachter.
Some interesting tidbits from the article:
Flickr had 400,000 (I'm assuming registered) users when they were acquired by Yahoo in March of last year and today they have over 5 million.
Comscore says Flickr is getting 18 million uniques a month (Outgoing Yahoo COO Dan Rosensweig had said Flickr gets 20 million uniques a month on Yahoo's last earnings conference call).
Comscore says Yahoo Photos is getting 41 million uniques a month.
From Stewart Butterfield: ""When you're growing at 70 percent per month, additional promotion from Yahoo isn't something we wanted," Butterfield said. Flickr needed to figure out how to deliver the right photos from hundreds of millions of images with billions of tags, he said."
From my own analysis, at least by one metric (number of photos online -- this info can be publicly obtained), Flickr grew by 9.16% last month. Flickr's growth (were it to run at the 70% number cited by Stewart monthly since their acquisition) would put their registered users at over 16 million vs. the 5 million reported today.
This might suggest that on a percentage basis Flickr's growth has significantly slowed. Still, Flickr is a machine adding roughly a little less than 1 million new photos a day on average to their service. Although the number of photos on the site pales in comparison to Photobucket and even even lags behind struggling Webshots, because of the emphasis placed on tagging and ranking photos combined with the power of their social network, Flickr probably has the singlemost significant collection of tagged, ranked and organized collection of photos that exists in the world today. This will likely yield significant advantage for Yahoo! image search once a successful integration of Flickr and Yahoo Image Search takes place.