You can see more information about Phase 4 at the ARIN press release. This is a huge deal for the Internet community and will likely change some corporate and enterprise adoption plans and thinking in the near future. If you are curious, it looks like Akamai was the big winner with the 126.96.36.199/10 allocation going to them and tipping the inventory level.
So for all of you holding off thinking IPv6 will never impact them, it is time to start planning and figuring out your design and implementation schedules. You will have a bit of time for the service providers to burn through their existing inventory of IPv4 but after that you will have to purchase IPv4 at the going market rate. It makes IPv6 look more and more attractive.
If you want some help getting started in a lab or deploying and you run Windows you might want to pick up my book.
Welcome to a brave new world, I think I need to pick up my "the world is ending" sign and go walk around downtown San Francisco for the day.