It's nice that mIRC finally has real IPv6 support and I'm using it as we speak.
Unfortunately, it's disabled in its default configuration and there is a "scary" warning in case you try to enable it. I believe this is wrong. Most applications with IPv6 support have it enabled by default, this includes Firefox, IE, and many others. In fact, I would say it's rare to disable it.
Disabling IPv6 by default makes it quite useless, since everyone will have IPv4 in the long-term future, but that address is very likely to be a private NAT-ed IP used by others as well.
The message claims that mIRC will not work correctly if you enable the IPv6 support if you don't have an IPv6 connection. If mIRC correctly resolves hostnames, for example by using getaddrinfo(), then it will prioritize IPv4 over IPv6 in case you are on 6to4 or you don't have a IPv6 address.
On Vista and later (and Linux), when the host doesn't have a IPv6 address getaddrinfo() only does A lookups. Most users don't have a IPv6 address and it wouldn't cause any problems.
Users should not have to care about IPv6 (or IPv4, for that matter). It should be seamless. If it has to be enabled explicitly, then no one will enable it. And if no one enables it, implementing IPv6 isn't really useful as you don't gain any of the advantages.
