The potaroo website publishes a report, generated daily, regarding the availability and predicted exhaustion of IPv4 space. The report contains several graphs highlighting the history of address allocations, allocation rates over time, projected allocations and projected address exhaustion dates. These graphs are reported from the perspective of IANA (Internet Assigned Numbers Authority) and the RIRs (Regional Internet Registries).
IANA serves essentially as the top of the IP food chain in allocating to RIRs from its pool of address space. Each of the RIRs then in turn allocates from its respective address space to Internet Service Providers (ISPs) and in some cases, legacy address space holders who've historically obtained address space directly from Network Information Centers (NICs) which preceeded RIRs. This is why the report indicates IANA running out of space first, followed within about a year of the RIRs running out. When IANA allocates its last block, an RIR will have received that block and possess that address capacity. As each RIR allocates space to ISPs, its pool will diminish and eventually exhaust.
Following the same logic then, ISPs will possess the capacity of the last RIR allocation, currently predicted to occur in late 2011. But quite possibly within a year of receiving this last IPv4 block of addresses, ISPs will likewise run out. This implies that anyone requesting IP address space from an ISP after this time, say late 2012, will have no choice but to implement IPv6 for Internet-accessible web or email servers. Any newly-formed organizations or those that require additional address space after this time will be "IPv6-only" organizations.
Perhaps you're thinking this is "not my problem" or I've got plenty of IPv4 space! But consider this: as this population of IPv6-only organizations and users grows into 2013 and beyond, will they be able to reach your websites and email? At some point in the future, you may receive a call from the business side of your organization inquiring as to why we're missing this growing segment of the market. If you await this call to begin your IPv6 planning, your response that you can enable IPv6 within a year may prove detrimental to your career prospects. It's prudent to begin now to learn about IPv6 technology, which infrastructure products in use on your network support or will support IPv6, and how you would implement IPv6 when needed. Having at least a basic project plan in place if you decide to defer implementation will enable you to answer that phone call with a much more palatable or even heroic answer!