ReadWriteWeb reports that John Curran, CEO of the American Registry of Internet Numbers (ARIN) believes that the Internet will be out of IP addresses in one year. The IPv4 countdown Twitter page states that we have "approximately" 343 days left.
Every IP version 4 address has a 32-bit number, which gives a maximum of some 4 billion unique IP addresses. IP version 6, on the other hand, uses a 128-bit address. This is enough to give every man, woman and child on earth some fifty-thousand trillion trillion IP addresses.
Right now, about 6% of IP v 4 addresses remain. The transition from v 4 to v 6 will not be a fast one, especially for companies like Google and Facebook who will have a ton of different addresses to move over. If things don't happen quite quickly enough, we could end up seeing a black market for IP addresses crop up for a short span of time.