"On February 3 , it finally happened: the clock ran out on the Internet as we know it. That was the day that the stash of Internet protocol addresses that are used to identify and locate computers connected to the Internet—the telephone numbers of the online world—was exhausted."
According to the Technology Review the current system for IP addresses, IPv4, uses numeric addresses that are 32 bit long. Which gives a total possible combination of 4 billion IP address. So with 7 billion people on this planet it's reasonable to believe we've ran out IP addresses. But don't worry. IPv6 is here with 48,000,000,000,000,000,000,000,000,000 IP address combination per person on this planet. We can't really blame the IPv4 people for their lack of foresight since they created IPv4 in 1981, when the Earth's population was much smaller, they even created IPv6 in 1986 well before the internet went public. However, the ISPs (AT&T, cable companies, Verizon, etc..) have been slow to adopt IPv6, we're lucky they stockpiled lots of IPv4 IP addressess here in the US...
Who does the Technolgy Review say should worry? Developing nations with booming internet user bases who insist on using IPv4.
For the full article, "clicky" here.