In the early days of IPV4 Internet, the only things online were large mainframes and a very few other, smaller machines. That grew to include PCs at work, and eventually PCs at home. Back then, it was still ok. Now, however, it's coming towards the finish line for IPV4 address, with everything from cell phones to PDAs to gaming consoles getting online, and estimates say that by 2012, 17 billion devices will be online. Roughly a third of the useable IPV4 addresses are left, and in many places, including the U.S., adoption of IPV6 is painfully slow. But when change doesn't come because it should, it eventually comes because it must:

A mandate from the Office of Management and Budget states all federal networks must have the ability to send and receive IPv6 packets by mid 2008. Only 30 percent of the Internet service provider networks, however, will support IPv6 by 2010, and 30 percent of user networks by 2012, according to a study by the National Institute of Standards and Technology (NIST) and the RTI International on IPv6 migration.
Even such, in all likelyhood the majority of addresses will be chewed up by home user devices, including the billions of handhelds, laptops, et cetera, that automatically hop online. No more IPV4 addresses in less than 6 years? It could happen. And in fact, it probably will!