One metric that could tell us how much traction IPv6 is gaining is to observe is the global routing table. As noted in this Ars Technica story, currently,the number of BGP-capable networks that are sending out an IPv6 announcement totals 34,214 for IPv4 and 2,090 for IPv6.
“The number of BGP-capable networks that are sending out an IPv6 announcement is a more useful measure, and this totals 34,214 for IPv4 and 2,090 for IPv6. So 6.1 percent of all networks have IPv6 enabled in their routers. This metric is expected to reach 80 percent by 2017 if current trends continue.
“Transit networks—ISPs that in turn have ISPs or other BGP-capable networks as their customers—have relatively high IPv6 deployment: 22 percent.
“Huston also looked at the ratio between the number of distinct IPv4 and IPv6 addresses seen by the Web servers of APNIC and its European counterpart RIPE. This ratio is now slightly over one percent. Caveats apply, however. Multiple IPv4 users may share an address through Network Address Translation while a single IPv6 user may be using different addresses over time due to address privacy mechanisms. Also, the Regional Internet Registries aren’t exactly mainstream Web destinations; their visitors are very likely more IPv6-capable than average.”