World IPv6 day is comming in June. Linux is ready. Comcast is using software based on the OpenWRT (based on Linux) router software in their IPv6 rapid deployment trial.
Linux is ready for IPv6 and has been for a long time. For years people have been working on disabling IPv6 support as things broke when it was enabled. Fortunately, most of these things have been fixed, and most systems run IPv6 with local link connectivity.
I have dual stack implementation using OpenWRT and Ubuntu running now. Due to lack of support by my ISP I am using a 6in4 tunnel I have written articles on Implementing IPv6 6to4 on OpenWRT and a followup Implementing IPv6 Part 2. The author of the Shorenet firewall has implemented an IPv6 firewall andd documents how to setup 6to4 and 6in6 tunnels.