If you listen to the buzz, the day of ipv4 exhaustion is nigh and operators need to be migrating en masse to ipv6. The problem with the v6 evangelism is that it doesn't take into account the complex incentives at work in the adoption of ipv6. A recent allocation by ARIN of a /9 block to U.S.-based network operator Comcast highlights this.
Comcast has been one of a handful of network operators publicly proclaiming their commitment to the deployment of ipv6. ARIN has been praising them for this. However, a few days ago ARIN dropped an enormous allocation of ipv4 addresses in Comcast's lap: approximately 8.4 million. The Comcast allocation drives home the point, overlooked by so many, that v6 deployment does not, at this stage of the game, decrease the demand for IPv4 addresses. Comcast is one of the most advanced v6 deployers in the United States and yet here it is gobbling up a huge chunk of the remaining v4 space. We'll note with some irony that the largest delegation ever seen by some was completed while there is ongoing debate in ARIN and other RIRs over how to ration the last /8.
Whether Comcast is being favored over other network operators is impossible to say without more information. But there does appear to be a contradiction between ARIN's member-driven Number Resource Policy Manual, which stipulates that organizations can request up to one year's supply of IP addresses, and Comcast's last three years of declining growth in high-speed Internet subscribers, which shows increases of about 1 million subscribers per year. (Last year, Comcast reported 1 million net additional subscribers, down from 1.3M in 2008, and 1.7M in 2007). However, Comcast also stated several years ago that it had exhausted (RFC 1918) address space used for internal management of its network. Needless to say, an allocation of more than 8 million addresses suggests further need for clarity around the incentives to migrate to IPv6.