The "no latency or speed penalty over IPv6" thing is true for me in San Francisco for major sites (Google, HE.net, Facebook, Wikipedia). Are you sure that you'

The "no latency or speed penalty over IPv6" thing is true for me in San Francisco for major sites (Google, HE.net, Facebook, Wikipedia). Are you sure that you're not running over a Teredo tunnel? (Is the IPv6 address you're handed in the 2601::/28 range [native IPv6 for Comcast], or is it in the 2001:0::/32 range [Teredo tunnel]?) Does some of your networking hardware handle IPv6 poorly? What happens when you plug in a IPv6-enabled computer directly into your cable modem?