Problem of practicality?
I'm of the impression that there are two main problems with IPv6:
1. Every legacy device that will not ever support it. I don't know about you, but there are certain devices that I am not willing to give up or stop using "just because all they know is IPv4".
That may be something of a moot point, with 6to4 routing and other sorts of solutions to the problem. I guess we'll see.
2. The bigger problem, at least as I see it, is knowing an IP address for a given machine. I have no trouble remembering something like 192.168.1.1 (or what-have-you) but do you really think that I'm going to remember 2001:db8:85a3::8a2e:370:7334 (cribbed from Wikipedia, for those who are wondering)?
Maybe that's not a problem either, given that the IPv6 implementation on the Macintosh (the only place I've seen it used so far) sets itself up automatically....?
For those of you with home routers and a mild-to-moderate sense of adventure, check to see if you can run DD-WRT on your hardware. DD-WRT does support IPv6, although I've never tried to use it. (I mention this only because it might keep a few dozen "unsupported" home routers/access points out of the bin for a while longer.)