it's a new combo port, combining the microphone and stereo headphones into 1 plug
i can see the elegance of doing away with the normal 2 plug system but am rough with my headphones and like being able to swap them around with mp3 player etc and replace when needed with stuff from the $1 shop
presumably headphones with the new plug won't be able to be swapped with older style units and won't be available for $1 for a few more years
Regular headphones still work in the same jack. iPods had the video output this way for a quite a while, until they realized they were losing money to those who just bought a cable at Best Buy, then they switched the output to the data port so you had to get a special/$50 cord from Apple.
