Every once in a while, a discussion about switching the Internet to IPv6 shows up somewhere. It's usually the same story about how on some date the world will run out of IP addresses, and the Internet will come crashing to a halt. Generally, these stories get it right because we really are running out of IP addresses. Unfortunately, switching to IPv6 is not simple at all, and it has nothing to do with technical reasons.
The fact that we're running out of IPv4 addresses makes them a scarce resource, and that's what holds back the switch. Scarcity makes them valuable. The IANA gains its power because they are scarce. ISPs can charge money for them because they are scarce. Your broadband provider controls how many systems you can easily use at one time, because they are scarce 1.
The scarcity of IPs gives power, and more importantly a revenue stream, to many organizations. The relatively unlimited number of IPv6 addresses renders them almost valueless, and destroys much of that power. Unfortunately, many of organizations responsible for making the switch are also the ones who gain from having that power. As a result, the switch is not happening very quickly.
There is some hope though. The White House Office of Management and Budget has declared that all Federal agencies must be using IPv6 by June 2008. Hopefully, this effort will spill over into the private sector as government contractors will also have to support it. However, this does not guaruntee that end users will see IPv6 addresses served from their cable modems any time soon.
Ultimately, adoption will be slow until it starts costing ISPs real money. Once that fire is lit, expect the switch to happen quickly.