Juniper points out that IPv6 provides a larger IP address space as well as native support for packet encryption, header authentication, IPsec virtual private networking, multicasting and dynamic address configuration. And it will solve quality of service, security, and network management issues that have bedeviled IT folks for a while.
Additionally, some estimates hold that current IP addresses may run out as soon as 2010. IPv6 will solve that problem by growing the IP space.
In other words, eat your spinach! It's good for you, no matter what it tastes like.
All this is true. But what's also true is that the transition to IPv6 can be nightmarish. Don't believe Juniper or others when they tell you the migration will be a smooth one. They have a vested interest in the matter. Moving to IPv6 means a big chance for them to sell lots more hardware and services.