Today, IANA announced that it had handed out two more /8 IPv4 assignments to APNIC. As a result, IANA is down to 5 /8s, triggering its special policy to hand out one address to each regional registrar (RIR). The 5 RIRs are AFRNIC (Africa), APNIC (Asia Pacific), ARIN (North America), LACNIC (Latin America) and RIPE (Europe). 
IANA hands IP address space to the RIRs in chunks of /8s, who then pass it on to ISPs, who then pass it on to end users. Some large end users may approach their RIR directly, and some legacy assignments are managed by IANA directly.
But in the end, what does this all mean?
(this FAQ is a work in progress)
A Quick FAQ To IPv4 Exhaustion
1 - Will the Internet stop working?
No. As a matter of fact, it is unlikely that the IPv4 internet will stop any time soon. It will likely happily exist next to the IPv6 internet. There are some transition mechanisms set up. While not pretty, the two internets can talk to each other via proxies and tunnels.
2 - Why do we run out of addresses?
IPv4 allows for about 4 billion addresses. There are about 6 billion people on the world... how many addresses do you need (phone, home, work...)? Its a simple math issue compounded by the fact that for efficient routing sake, we can't assign all addresses.
3 - A lot of IPv4 space is still unused. Why don't we use it more effectively?
The problem is not just that we are running out of addresses, even though that is the killer issue here. Assigning addresses more effectively would mean that assignments would become smaller and routing tables would become more complex. In order to make this work, we would have to essentially renumberthe internet, and still be out of addresses at some point.
4 - What about legacy space? Does Apple really need a /8?
In the beginning of the Internet, IPv4 address space was handed out very liberally. Remember it was just an experiment? Some of the original participants still have large IPv4 assignments which they don't use efficiently. However, even if all of them are handed back, it would delay the problem only by 1-2 years at great expense to the effected companies (and they have contracts giving them the rights to use the address space). Some legacy allocations have been returned in the past
5 - What do I need to do today?
Relax. Nothing is going to happen fast. the RIRs still have space left, depending on the region a few month to a year. After that, it will get tricky. You may already find it harder to get IP address space. Eventually, your ISP may ask for some space back as they can't get new addresses from the RIR. Over time, IPv4 will get more expensive then IPv6.
6 - So I can just wait and do nothing?
No. What you should do tomorrow (maybe today?) is setup a test lab to familiarize yourself with IPv6. It is easy to get going. Ask your ISPif they support it (or when), or setup a tunnel with a free tunnel provider like Hurricane Electric  or Sixxs  (there are others). You need a plan on how to deal with it. Even if you don't need IPv6, maybe your business partners start using it and you need to connect to them via IPv6.
7 - Can't I just ignore it?
Remember why you are using IP in the first place? It allows you to connect to customers, suppliers, branch offices. In short:It keeps you in business. Once these people expect IPv6 connectivity, you will likely have to move along with it. It is like any technology in that it ultimately has to support the business (and well... it is fun too!).
8 - What will change from a security point of view?
Everything and nothing. The most important change is probably the fact that NAT will become less important. Endpoint protection and carefully configured firewalls will become more important. Passive asset detection will become more important compared to active scanning. There is a lot of security gear you own that probably does a lousy job dealing with IPv6. Did I mention it requires a plan and testing?
Johannes B. Ullrich, Ph.D.
SANS Technology Institute
(c) SANS Internet Storm Center. http://isc.sans.org Creative Commons Attribution-Noncommercial 3.0 United States License.