Exploring the software behind Facebook

 * Facebook serves 570 billion page views per month (according to Google Ad Planner).
    * There are more photos on Facebook than all other photo sites combined (including sites like Flickr).
    * More than 3 billion photos are uploaded every month.
    * Facebook’s systems serve 1.2 million photos per second. This doesn’t include the images served by Facebook’s CDN.
    * More than 25 billion pieces of content (status updates, comments, etc) are shared every month.
    * Facebook has more than 30,000 servers (and this number is from last year!)

http://royal.pingdom.com/2010/06/18/the-software-behind-facebook/