Turning IPv6 off now just means you have to turn it on in a few months. I would rather avoid making two changes to all the hosts in my network.
The simpler solution for the basic network where IPv6 doesn't matter yet is to make sure your router null routes the IPv6 default (::/0), get valid IPv6 addresses, build a basic subnetting plan and put it in place on your routers with appropriate RAs. That will prevent hosts from trying to build 6to4 or Teredo or ISATAP or other bizarre kinds of autotunnels and give quick negative responses to attempts to reach IPv6 hosts resulting in timely fallback to IPv4. Simple, efficient, and, when you do actually need IPv6 connectivity, you just need to change the configuration on your routers (which you'd have to do anyway).
As to when to deploy IPv6, if you're running a network full of end users behind an IPv4 NAT using RFC-1918 space, then, no, you probably don't need to convert that network over right away, but, you will want to deal with all those systems that are now shipping with IPv6 on by default as I have described above or you will see user complaints as a result of their attempts to reach a growing mass of IPv6 content.
However, if you have any public facing content or services (as most businesses do at this point), then, you're going to want to make sure that those are reachable via IPv6 as well as IPv4 as soon as possible. Certainly within the next 12 months or so.
The people depending on the current address calculators and an 18-month clock to RIR runout after IANA exhaustion are in for some rude awakenings.
First, the clocks are wrong. They don't seem to correctly account for current utilization rates, nor do they account for the fact that 5 of the 14 remaining
IPv4 /8s are reserved to be distributed one to each regional internet registry when the others are exhausted.
At the beginning of 2010, there were 21 IPv4 /8s in the IANA IPv4 free pool and 5 in the reserved section described in the last paragraph. Today, less than 9 months later, there are only 9 /8s remaining in the IANA free pool and 5 still in the reserved section. (Note that the clocks all talk about 14/224 which is 9+5).
At the current rate of consumption, we're not talking about 285 days to IANA runout, we're talking January or February of 2011. Feb. 28, 2011 is 194 days from now in my current timezone (Thursday, 20 September, 2010). (Notice the 91 day (or more) error in the countdown clock).
Additionally, once IANA runs out of IPv4, the RIRs aren't going to simply coast for 18 moths. APNIC, RIPE, and ARIN will likely be in a race to see who runs out first. I think the smart money is on APNIC. However, whichever one runs out first, you can bet that the multinationals (i.e. the largest consumers of IPv4 addresses) in any one of those three regions will start pulling space from the other regions too. As a result, whichever one runs out first will accelerate the other two rather abruptly. I predict that the first RIR will run out on a timeframe more like 6 months after IANA exhaustion rather than 18.
It's less clear what will happen with space in the AfriNIC and LACNIC regions due to unique circumstances.
IPv6 is no longer an option, it is a requirement. Time to stop with the FUD and misinformation and start facing the cold hard facts staring us in the face.
Yes, the earliest predictions of runout turned out to be wrong (only because NAT was developed _AFTER_ those predictions were issued, btw).
However, the predictions today are mostly wrong too, but, not in the direction you want and certainly not as far off.
Failure to deploy IPv6 at least to your public content and services within the next 12 months will place you at a competitive disadvantage against other companies that do. That disadvantage will only increase with time. It is also critical to deploy IPv6 capabilities to your support staff and your IT
departments so that they can become familiar with it and learn to troubleshoot it and assist customers with IPv6 related problems.
About the author of this comment: Owen DeLong is an IPv6 Evangelist at Hurricane Electric and an elected member of the ARIN Advisory Council. His statement here is not an official statement of ARIN or the Advisory council, but, his participation on that council keeps him keenly aware of the state of the IPv4 free pool and the issues surrounding IPv6 transition and IPv4 exhaustion.