Comcast's idea is to allow many broadband customers to share one global IPv4 address instead of providing one global IPv4 address per customer.

"The exact ratio of IPv4 addresses to customers is something we are studying right now," Durand says. "We are working on some tests to see if it is 1-to-5, or 1-to-100 or 1-to-200."

The trick with sharing public IPv4 addresses among many customers is doing it in the simplest way, Durand says.

said by TK Junk Mail :

... multiple users sharing an IPV4 address.

for RIAA/MPAA watchdogs that track users by IP address; etc. If multiple users are using the same IP address, how are they going to police things with existing systems.