The American Registry for Internet Numbers (ARIN) says the amount of available IPv4 addresses is running short and says it's time to migrate to IPv6. Currently 68% of the IPv4 addresses have already been allocated, 13% is unavailable and only 19% is still free.
The organization doesn't want to make predictions on when the supply of IPv4 addresses will run out, choosing instead to monitor distribution and consumption trends so that others can do the predicting.
Forecasts predict IPv4 addresses will run out as soon as 2010.
It's certainly possible that the remaining 48 blocks of 16.78 million IPv4 addresses in the global pool will be used up by 2010. However, ARIN and its counterparts across the globe each hold about two years' worth of address space to allow for day-to-day operation. This brings the total amount of free address space to the equivalent of 72 blocks. In both 2005 and 2006 ten of those blocks were used up, but so far this year, the rate of usage seems to be increasing somewhat.