The limited address space is the real problem and the shortage has been leading networking issues for years. IPv6's extra space, the minimum subnet of /64 and the large rfc1918 eqivalent space will make things lots easier.
How often has somebody allocated a /30 for a routing/firewall segment that then needed HA some years later (2 real addresses and a floating). The /30 is then wasted because its to small to be useful without making a mess of routing.
In around two years it will be impossible to get portable address space allocated. If I have the next big killer application I'll be tied to whatever single ISP wants to rent some address space to me. If they have routing problems I won't be able to fail my routes over to somebody else.
I've seen a client fill a B class network. They built their addressing scheme many years ago when Bs were still given out and in the years since grew in ways they hadn't predicted. Of course some of their server farms turned out much bigger, some of their locations turned out smaller than planned wasting space. Basically they ended up with a mess that was difficult to clean up. IPv6 won't get to that sort of fragmentation since /64s will always be useful.
I've seen many situations where large organisations use 10/8 for their internal networks. They then merge, split or go partnership with somebody that requires private links between the organisations. I've seen situation where application servers that needed to talk to each other were on the same 10.x.y.z and the NAT nightmare between them sucked. Every device had a different address depending on who you talked to.
People talk about IBM should give back their A. Without that A there would be a NAT nightmare between everybody that IBM connects to for their management services. Imagine how many 10/8 networks IBMs NOC talks to and imagine what it would be like if they were also 10/8.
I can imagine all the big companies moving to public v6 address space for their private networks but never advertising it to the Internet. The outbound traffic will be NATed/proxied at the gateway. This will make the corporate merge/split/peer cycle easier to deal with.