When Will We Run Out of IPv4 Address?
Of course that is quite literally the $1 million question that for various nobody could possibly predict with 100% accuracy. Here are some of the best of technical attempts to answer the question.
http://www.potaroo.net/tools/ipv4/index.html
http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_8-3/ipv4.html