Given that IPv4 addresses are a finite resource, we can expect concerns over their distribution to increase in the coming years.
The internet, which was developed by the US government, is administered largely by the Internet Corporation for Assigned Names and Numbers (Icann), which controls the assignment of IP addresses through the Internet Assigned Numbers Authority (Iana).
Icann was formed in 1998, when it began controlling the internet. It allocates IP addresses to five regional internet registries (RIRs), which then allocate them to ISPs and other organisations.
At the Iana/RIR level, IP addresses are generally awarded in blocks of 224 addresses (over 16 million addresses at once), known as /8 blocks. As RIRs allocate the addresses further down the food chain, they try to ensure that as many of them are used as possible.
There are some address hogs at the institutional level, but these are largely due to historical factors. For example, the Massachusetts Institute of Technology has 16.7 million addresses to itself, but this is because in the early days of the internet, it was only possible to allocate /8 blocks of addresses. Now, RIRs can split them into smaller chunks.
These days, addresses are allocated to RIRs in a reasonably egalitarian way, partly because there are still a reasonable number left. At the end of 2004, according to a report on IPv4 address space by Geoff Huston, treasurer of the executive committee at Asia Pacific RIR Apnic, 51% of the blocks have already been assigned, with 34% sitting in Iana and RIR registries. The rest are either reserved for use elsewhere or used for multicasting purposes.
Based on projections from historical data, Huston's report predicts the exhaustion of the IPv4 unallocated address pool some time in May 2013, which will probably be accompanied by the opening of trading markets as IP addresses become more valuable.
Notwithstanding such measures, Huston foresees the complete exhaustion of the IPv4 address space in October 2022.