A while ago I was asked to write an article about IPv6 training. I could just cover the training aspect, like what's offered (answer: not much) and whether someone can train the whole operations team like you could in the IPv4 or MPLS/VPN world (answer: no), but I wanted to understand whether anyone is really using IPv6 in a production network. I found a few academic networks (after all, there are about 2000 IPv6 prefixes assigned and someone should be doing something with them), but not much of what I would call a real production environment, which is a bad thing, as it looks like the IPv4 address space will get saturated in a few years.
Update 2010-03-12: Numerous commercial ISPs now offer native IPv6 connectivity, but they also face significant deployment challenges. You will find an overview of those in my Market trends in Service Provider networks workshop (register for the online webinar). Advanced backbone designs and configurations are explained in the Building IPv6 Service Provider core workshop (register for the online webinar).
My conclusions are summarized in the article I wrote for SearchTelecom.com. I still have mixed feelings about our ability to be IPv6-ready when needed (as well as when we'll need it). At the very least, if you're running an enterprise network, there's no need to rush (unless, of course, there are tax breaks or incentives on the horizon); unless you decide to deploy IPv6 internally (hopefully for a good reason), the first time you'll meet it is when you'll deploy dual stack on your public servers to avoid NATing to IPv6-only clients on the public Internet.
Of course, I can be completely wrong, in which case I would highly appreciate your corrections.