Every connection with the Internet has to have a unique number (the IP address). This is because whenever any piece of data is sent across the Internet, it has to have the number of the connection where it is going to. There will be one number for your home broadband connection, one for my home broadband connection, one (or more) for any website you go to, etc.
These numbers are drawn from a pool of about 3.5 billion numbers.
The worldwide master pool is operated by IANA. IANA gives out blocks of numbers to five groups serving Africa; North America; South America; Asia Pacific; and Europe, the Middle East and Central Asia. These groups in turn hand out blocks of numbers to either national bodies or smaller bodies such as ISPs, and eventually numbers get assigned to individual connections.
What happened yesterday (3 Feb 2011) was that the master pool completely ran out of spare numbers.
IANA no longer has any spare numbers to hand out to the five groups it serves.
That doesn't mean there aren't any spare numbers, but rather that any spare numbers are now in the hands of the five regional groups and the smaller groups below them.
The number of spare numbers is declining. Fundamentally, there was no "step" reduction yesterday (3 Feb 2011) in the number of spare numbers available, so in theory it is not really news, but the fact that the global authority IANA no longer has any spare to dish out is considered by many to be a significant milestone or marker in the decline of the Internet addressing system.
Over time, the shortage of spare numbers will hamper the setting-up of new connections.
This issue has not gone unanticipated. By way of of a solution, in 1998, the boffins came up with a new way of operating the Internet called IPv6, which stands for the Internet Protocol version 6. (By way of background, the current way of operating the Internet is called IPv4.)
Amongst other benefits, IPv6 uses a much larger range of numbers to assign unique numbers to each connection. Whereas IPv4 has some 3.5 billion available numbers to assign to connections, IPv6 initially has sufficient space for about 2 billion billion connections (for geeks: I am assuming the first nybble is 2 or 3, and every connection is assigned a /64).
Unfortunately, we can't just switch on IPv6 and everything's peachy again. For IPv6 to work, the computers talking to each other must both talk IPv6, and the intervening bits of Internet must also be compatible with IPv6.
Fortunately IPv6 and IPv4 can happily coexist on computers, and on the Internet in between them. Fortunately again, most of the stuff you usually use like web browsing and e-mail has already been upgraded to be compatible with IPv6 and will automatically use IPv4 or IPv6 depending on what's available. So for the ordinary person, there should not be much in the way of a noticeable difference.
So many people expect that the way forward will be for the existing IPv4 operations to move to combined IPv4 and IPv6 operations. Eventually we should get to a tipping point where more-or-less everything works fine with IPv6 and we can start dropping the old IPv4 system.
The problem is that there is some resistance amongst ISP to adopting IPv6 alongside IPv4. It seems that most ISPs seem to be waiting until there is a "brick wall" problem in front of their nose, at which point they will start running round like headless chickens trying to fix things.
Now, IPv6 is by no means a new technology. It has been live in many places for many years. The problem is that it will take time for people new to the subject to get their knowledge up to speed, systems to be upgraded, problems to shake out etc. and this will take months to years. If ISPs wait until the last minute, then it isn't going to work.
So there are various people trying to make noise, raise awareness etc.
We shall see.