>IPv6 can be adopted without a performance penalty
Sadly, in my case, this is untrue. If I enable v6 on my Comcast home connection, I see routes with consistently higher latency--around 50ms more for paths within the U.S. such that even a 200 mile destination (HSV => ATL) is ~70ms away.
You should probably go to forums.comcast.net and post some traceroutes. There's no latency penalty from the SF bay area, and Alabama seems like the kind of place that's easily overlooked.
Sorry, but this is untrue for me. I have Comcast, and if I enable IPv6 from my home in Santa Clara county, I also start seeing large increases in latency and significantly slower download speeds.
I haven't bothered posting on the Comcast forums. I simply disable IPv6 and get on with my life. Maybe I'll give it a try in another few months.
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?
I have comcast. My router is configured to enable IPv6, and my local machine appears to have an IPv6 address (though it appears to just be an IPv4 compatibility address, as it contains my IPv4 address with an fffe in the middle). But this site claims I don't have an IPv6 address: http://test-ipv6.com/
They have actually started working with business class customers this year. I'm still, rather impatiently at this point, waiting for it to trickle down to residential customers.
They have a landing page[0] that hints at the possibility, but I've never seen anything or heard anyone actually say that IPv6 is coming to residential customers.
They haven't bothered to update that page in a few years, sadly. It says "Dual Stack IPv4/IPv6 will be launched in various areas within Verizon’s FiOS network, starting Later in 2012. Check back for more information."
Sadly, in my case, this is untrue. If I enable v6 on my Comcast home connection, I see routes with consistently higher latency--around 50ms more for paths within the U.S. such that even a 200 mile destination (HSV => ATL) is ~70ms away.