The internet protocol version 4 address space has around 4.3 billion addresses. The Internet Assigned Numbers Authority has divided those up into 256 blocks of around 16.7 million addresses each. As of October 2010, only 12 of those blocks remained.
Here was XKCD’s map of the internet as of 2006:
And here’s a map of where we were at in October (only white coloured squares are available, the others are colour coded by the year they were assigned):
Turns out as of yesterday there are only 6 of these blocks left. And two of them are about to get claimed by ARIN. It looks like IANA will run out of blocks by February, after the last four are claimed by RIPE and APNIC. The various Regional Internet Registries will run down their remaining allocations, and by around June of next year there will be no more addresses left! Quite the end of an era, really. Good thing everyone’s ready to make the switch to IPv6*!
* everyone is definitely not ready to make the switch to IPv6.