Re: I'm invoking my rule again @Lee D
Actually, basically all GMail SMTP traffic and Google search comes in and out on IPv6. I'm sure if you switched off GMail and Google for your users they'd be up in arms so, just on it's own, that's a fair chunk.
Lots of mobile networks and protocols are IPv6-only - you'll see a ton of iPhone/iPad access if you switch it on.
Apart from that, it RELIES ON WEBSITES TO DEPLOY IT FIRST, which is exactly my concern. It's like those old banking websites that used to tell you that Firefox isn't supported because "nobody uses it to access our website"... of course not, you morons - how can you access a website that specifically does not support Firefox in the first place?
IPv6 isn't going away. And it's literally a day or two's work to turn it on for your main public-facing services (enable it, add entries in firewalls and configurations for it - THEY ALL SUPPORT IT ALREADY - stick entries in your DNS for it, and you'll spot that google's DNS, SMTP and HTTP servers instantly start talking to you over IPv6.