I've been learning more about IPv6, and am getting to the point where I'm going to be implementing an IPv6 lab to test various technologies that our company relies on, so that I can re-engineer them now, if necessary, for a future IPv6 switchover.
My plan is that in a year and a half, we're able to run fully IPv6 inside the network, and that we'll be running dual-stacks for client access. I've decided a year and a half so that I have 6 full months of testing and planning, and run the "hot" side of our infrastructure as IPv6 for 6 months while the "warm" side is IPv4, and after 6 months, convert the "warm" to IPv6. That will give me a testing, go live, and fall back point.
I'm interested to hear how other people are solving this problem, and what your roll-out plan looks like.
@Evan: My business reason is foresight. Eventually it's going to be necessary to have IPv6 if you want new network blocks. Eventually, my clients will be on IPv6. Eventually, everyone is going to be on IPv6. I want to convert before we're forced to convert, and I want to be able to do it on my terms, rather than under pressure from some regulatory agency.
Gerald Combs makes a great point. Emerging markets are not going to be able to get IPv4 blocks in the volume that they'd need, so at a point in the near future, and far sooner than established infrastructures, they're going to be using IPv6 regularly. Anyone with international clients or in a market that shows growth potential in the world economy may want to step it up.