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As impressive as four billion photos is, that figure is trounced by Facebook, which reported more than 15 billion photos in its database back in April and currently adds two billion more photos each month.
Founded in 2004 and acquired by Yahoo! in 2005, Flickr remains a prime destination for photo lovers. Still, the lure of unlimited photo uploads and an expanded userbase (plus tagging!) has led many users off to Facebook's pastures.
Do you still use Flickr as much as you used to? What's your favorite photo sharing service?