IPv4 will reach its limits within a couple of years and it's pretty shocking that IPv6 is still barely used. ARS Technica reports only 0.0026 percent of the total traffic on the Internet is IPv6 traffic:
Arbor Networks, a supplier of "secure service control solutions," cooperated with some 90 ISPs and other organizations running large networks to find out more about how much IPv6 traffic is really flowing over the Internet. They measured traffic flowing through almost 2,400 routers, amounting to no less than 4.5 terabits per second. The results: about 12 megabits of Teredo traffic, which was about 10 percent of the protocol 41 traffic, for a total of some 117Mbps. The amount of native IPv6 traffic was "negligible" but only an unknown fraction of the measuring routers was able to report native IPv6 measurements.
The report cites studies that estimate the amount of native IPv6 traffic as 10 to 75 percent, so the total amount of IPv6 traffic would be 130 to 470Mbps. The measured IPv6 traffic constitutes 0.0026 percent of the total traffic. (The report rounds down the numbers to 4Tbps total and 0.002 percent IPv6.) IPv6 traffic has increased over the year that measurements were done, but so has IPv4 traffic; the percentage has remained the same.
However, the author notes that the study failed to count most native IPv6 traffic. He refers to numbers from the Amsterdam Internet Exchange which indicate about 0.12 percent of the traffic is IPv6 traffic. That's a lot higher but it's still next to nothing.