I can do IPv6 from my ISP since last November. My issues so far have been:
- The ISP ADSL router hasn't been extensively tested for IPv6. Its caching DNS server tends to die after approximately 10 days, and the IPv6 connection itself is at times unavailable (probably not an up-link issue as rebooting the ADSL router fixes the issue. Temporarily.)
- Some web sites have registered a DNS entry for IPv6, but don't have a properly configured IPv6 HTTP server. I could ask the DNS resolver to try IPv4 first, but then when would I actually be using IPv6 ?
- I can't even experience the non-NAT'ed network, as I don't have IPv6 access from the work place.
On the other hand, IPv6 was doing fine 12 years ago, on the IPv6 backbone from the university.