At my workplace we've been doing some limited trials of providing IPv6 connectivity to internal systems (we don't have much in the way of outward facing stuff).
IMHO, and I would love to be corrected on this, but as far as I can see, there are some big problems to overcome with corporate deployments (not so much with home connections). Note that I am in no way advocating sticking with IPv4, this is just from my experiences so far:
It starts with the fact that your internal IP addresses will be determined by what your ISP gives you. What if you change ISPs? This means renumbering everything. Changing ISPs didn't used to mean that. What's the solution - use address autoconfiguration everywhere? That's not going to scale up very well. Think about DNS. Dynamic DNS updates? Over potentially thousands of hosts? And keeping all that secure? Sounds like a disaster waiting to happen.
OK, so if you're running a network that big, you probably want to get some provider-independent address space, then you keep the same address scheme and advertise your addresses out to your ISP. That way your addresses always stay the same no matter which ISP you use and you also have the option to multi-home. All well and good, but acquiring PI addresses still requires you to become a member of your local RIR; it's quite a paperwork-intensive process. With IPv4 this is acceptable as it's mostly only large enterprises and ISPs that need PI space and the number of RIR members remains low. With IPv6, medium and small companies will also have an urgent requirement for PI space. The process needs to be simplified, packaged up, and probably most importantly, delegated; will the RIRs be able to cope as it stands? We will end up with huge waiting lists to get address space. The process needs to be more like registering a domain than getting PI IPv4 space.
Now, of course, once so many more organisations are using PI addresses, what does this mean for the size of the global routing table? This is more of a problem for the ISPs and router vendors than the end users, but a problem nonetheless.
Can anyone more experienced in IPv6 than me refute these points?