I do not think any company will willingly give up their address space in IPv4 - Even way past 2010 this will still be considered the Real and reliable Net. I forsee interopability problems for several years after more global adoption of IPv6.
I think one deterent not discussed is that IPv6 does not seem to force any authentication and therefore does nothing to reduce DDoS attacks. It also (even if this is not true) has the appearance to the public, of only being a change to add more IP address space, as long is this is the public preception there will be no effort to move to it while IP address space is available.
Another factor is the inevitable change from 1000's of start up ISP's to 5-10 giant world wide corps that "own" most of the internets network space. These larger networks will have more need for things like AS numbers than public IP addresses, so this congealing of networks should reduce the need for so many public IP addresses, but again unless forced, I don't see any large ISP giving up their IPv4 space willingly.

I think it is obvious that IANA/ICAAN will need to come up with some stricter rules and enforcement for IPv4 address space ownership over the next year.