Arbor Networks released the results of a study on IPv6 usage. Highlights:
During the six month study period, IPv4 inter-domain traffic grew by an average of 40-60%. In marked contrast, IPv6 (both native and tunneled) decreased by an average 12%, though the small volumes of native IPv6 more than doubled.
That is, while the last IPv4 block was being allocated to a registry, IPv6 traffic not only failed to keep up with IPv4 traffic growth, it decreased in absolute terms! Hardly the sign of a technology on a successful adoption curve. Combined IPv6 traffic (native and tunneled) accounted for just 0.1% to 0.2% of traffic on the carriers studied.
...P2P continues to dominate at more than 60% of all IPv6 traffic. Note that our analysis primarily used well-known port numbers. Unlike IPv4 P2P, the data suggests most IPv6 P2P application makes little effort to encrypt or use randomized ports. This IPv6 P2P behavior may correspond to the relative lack of IPv6 capable firewall and traffic management solutions. At a distant second and third, Web and SSH both average 4.6% of IPv6 traffic.
In contrast, IPv4 traffic is primarily attributable to a few large services: Netflix 20%, YouTube 12%, Bittorrent 8%. Flash and other HTTP video are about 6% each; conventional HTTP traffic is 19%. (I suppose this could be viewed as good news--- heavy usage of IPv6 will occur if any of one of these services start to be widely accessed using IPv6.)
My guess as to why P2P services are so popular on IPv6 is that it allows true peering. For most protocols, one endpoint or the other has to be reachable by a global IPv4 address (not both can be behind NAT.) Running IPv6 lets you access a greater population of peers, and thus get better download speeds (and probably better sharing ratios, if that's important?) So if you're running file-sharing P2P apps, and stuck behind a NAT, a network-savvy user can gain some benefit by setting things up appropriately.
The top five tunnel end points contribute more than 90% of all tunneled IPv6 traffic. These top end points include the Anycast address (126.96.36.199) followed by Hurricane Electric tunnel broker ranges and Microsoft’s Teredo (188.8.131.52).
Native IPv6 is only about 20% of IPv6 traffic. The rest has to be tunneled. I would bet that most of the anycast traffic is actually going to one of the other top-five points. My ISP, for example, sends such packets to Hurricane Electric's tunnel broker. It would be interesting to see the breakdown of this, but I suspect the implication is that much IPv6 traffic has to be routed considerably out of its 'shortest path' to the true destination, with all the attendant vulnerability to delay, loss, and congestion.
"World IPv6 Day" is a flag day where major internet services will enable IPv6 by "default" (presumably on their primary domain name rather than an IPv6 subdomain):
In a remarkable, first of a kind global experiment, providers around the world will enable IPv6 by default on most of the major popular Internet web sites this June 8th. Previously, large content providers generally proved reluctant to enable v6 by default over concerns of poor performance and disruptions to customer traffic. In short, content providers feared that unilaterally enabling v6 put their web sites at a competitive disadvantage.
World v6 Day represents the first global experiment in new Internet technologies. What will happen on v6 day? Will the flood of IPv6 traffic result in network failures? Will operators and vendors discover critical bugs in network infrastructure? As an industry, we’re not sure -– that is why this V6 day experiment is so crucial.
This is exactly why IPv4 will be around (approximately) forever--- the Internet is too important to run global experiments on, in order to figure out whether the 15-year-old next generation technology can actually be made to work.