we are running out of IP addressess because of ARIN giving out class b's and C's like candy on halloween back in the old days. now the damage has been done and no candy is left. If ARIN was more conservatives in assigning ip's, we would have a lot more class c's and b's availible. period.
ipv6 should provide us with limitless ips, but at the expense of millions of man hours converting routers, switches, internetworking equipment in general to it.