Lars Eggert tracks deployment trends for IPv6, DNSSEC, SIP, XMPP and a few other protocols at:
In his “experiment,” Lars is tracking the top 500 sites from Alexa.com both overall and for individual countries, and then performing a variety of tests on them to determine IPv6 accessibility. As he writes (our emphasis):
This experiment attempts to answer the following question: If an average user had a working installation of IPv6 on their machine, how useful would it be to them? What percentage of the services and sites the average user regularly accesses are IPv6-enabled? In other words, the experiment attempts to quantify the usefulness of IPv6 to the average end user, given the current deployment of IPv6 in the Internet.
The experiment does not track how many users or hosts use IPv6 in the current Internet. It also does not track how many sites have configurations of IPv6 that are not accessible by average users from the Internet.
If you go on down the page, Lars includes some interesting IPv6 trend data going back to when he started collecting the data in October 2007. Lars also includes statistics on DNSSEC deployment as well as that of a few other protocols.