Ars Technica On IP Addresses

There are 3,706,650,624 usable IPv4 addresses. On January 1, 2000, approximately 1,615 million (44 percent) were in use and 2,092 million were still available. Today, ten years later, 2,985 million addresses (81 percent) are in use, and 722 million are still free. In that time, the number of addresses used per year increased from 79 million in 2000 to 203 million in 2009. So it’s a near certainty that before Barack Obama vacates the White House, we’ll be out of IPv4 address. (Even if he doesn’t get re-elected.)

via A decade’s worth of IPv4 addresses.