The chart below shows that since March 2001 IP address counts have not increased significantly, while computers have broadly sustained an increasing trend, other than for the Code Red and Nimda dip in 2001. This primarily reflects increased use of HTTP 1.1 virtual hosting which can share an IP address. Since the survey started in 1999, IP addresses have not quite doubled, while computer numbers have more than quadrupled. Since March 2001 computer numbers have increased 84.3%, yet IP addresses only by 7.9%.
The methodology is described in the Hosting Provider Server Count.