At the top level the major transit networks support IPv6 and most of them have for years.
At the bottom level the end devices mostly support IPv6 though XP systems (which are still scarilly common) have it disabled by default
The problem comes in the middle, access providers and corporate network operators need to do the work to give the IPv6 capable devices they and their customers own access to the IPv6 internet. Many of them don't see doing so as a priority.
MS implemented a protocol called teredo to work arround this but it's fragile because it fights nat rather than working with it. It's also disabled by default on networks where a domain controller is detected (presumablly because MS didn't want to be accused of subverting corporate firewalls).
Most operating systems will preffer IPv6 when a native v6 connection is available and yet the ipv6 traffic as reported by the likes of google is in the single digit percentages.
Unfortunately I'm struggling to find good stats on how many users can access v6 only resources even though they preffer v4. Test-ipv6 has some stats but I don't consider them representitive of normal users. I remember seeing some stats a while back that said it was about half but I don't remember where