The number of websites in the Internet has been rising exponentially reaching 525,998,433 as on November 2011 according to data from Netcraft. Although the number of websites have doubled in 2011 alone, not all of these websites are active. Also, this number doesn't represent the number of domains registered as there are many websites which are created as sub-domains such as Google's Blogspot or Wordpress.
Here is a simple poster from ROI Media explaining the anatomy of any common modern website and some statistics on how folks are using the Internet. Please do add in your bits as comments.