Arbor has an awesome rant on the state of practical IPv4 to IPv6 conversion:
Recall that IPv4 address space exhaustion is imminent, with free pool exhaustion predictions, ... from the Regional Internet Registries (RIRs) to occur around mid-2012 - only ~1100 days away.
Compare the development paths of IP and BGP; the relevant groups spec'd out BGP4 and IPv6 at roughly the same time (1994), however in terms of adoption, BGP4 clearly wins. Why'd that happen? 1) BGP4 offered more control, and 2) deploying it only involved convincing your neighbor to run it. Looking at IPv4 and IPv6, you don't get much more than what you already have, and deploying it requires non-local coordination. So, IPv6 remains the red-headed stepchild you kick around because you can't disown it.