Good (not stupid) question. The level of effort [pain] is a question that we all ask when facing the unknown. From the perspective of someone who has led the successful IPv6 implementation in a major global enterprise, IPv6 is a lot easier that past network protocol changes we endured. Any yes, I have gone through SNA/SDLC, HDLC, DECnet, IPX, and Vines transitions. Here are some observations

IPv6 built into the HOST OS
Bechtel’s implementation used Windows XP and Windows Server 2003 as primary hosts for enabling IPv6. The process is straight forward enable IPv6, turn off unneeded transition tunnels. With previous technologies, the network protocol was an add-on. IPv6 is on by default in Vista and Windows Server 2008.

Network OS Support
Cisco IOS, JUNOS, and other popular network operating systems have supported IPv6 for a while. Juniper has IPv6 enabled by default on a majority of their products. Cisco does not. In both cases the capabilities are there. Since IPv6 and IPv6 share common ports, port-based rules can apply to both protocols; i.e. block port 80, allow port 443. Routing paradigms are also comfortably parallel and/or converged. OSPFv3 (IPv6) and OSPFv2 (IPv4)

Common Naming Infrastructure
Both IPv4 and IPv6 use DNS as a common naming / locating infrastructure. AAAA resource records for IPv6 complement the “A” resource records for IPv4 allowing a host to be easily located using wither protocol.

Protocol Translation Avoidance
Bechtel’s approach is ubiquitous dual-stack for the next several years. While there may be a slight administrative overhead with this approach, it has removed the need to implement host-based or network-based protocol translators. If you have had networks running DECnet, IPX, SNA, and IPv4 concurrently, you’ll REALLY appreciate the significance of this.

Addressing
IPv6 addresses provide a lot more flexibility, but also require some new thought processes. In the transition from DECnet to TCI/IP, some companies applied the DECnet area paradigm to their new IPv4 network topology. While this may have made their mental transition a bit easier, this was not necessarily a smart strategic move. Implementation of IPv6 in an IPv4 environment will be easier, but there are opportunities with IPv6 addressing that must be understood and implemented early, if possible. IPv6 multicast and Mobile IPv6 are a couple of examples. In 2005 we learned, discussed, and debated Bechtel’s IPv6 numbering plan for months before settling on a final approach.

Stop the Bleeding
One of the many suggestions in our book, Global IPv6 Strategies, is to stop purchasing / developing products that are not IPv6 aware. Perpetuating a dependence on IPv4 in now a wise thing with broader global deployment of IPv6 already starting.