My main concerns are: Roughly how many users are going to share one public IP? Is this going to break bittorrent, Skype, or other p2p applications? If yes, how could an ISP ever get away with it? Millions of people use these applications every day. There are privacy concerns as well: if someone sharing a public IP with me does something nasty on the internet, could I be dragged into it? Sounds scary. Also, I'm an avid gamer, and many of my online games have servers that ban hackers by IP — I assume I would get banned along with them?
Finally, if all of the above fears prove true, do you think that ISPs are still actually going to roll with massive NAT-ing?