Amongst the many features of the PR1.1 software update, one of the most important from developers' perspective is the availability of Near Field Communications. Even though the API remains the same, the NFC stack has been significantly updated.
Its usefulness was quite limited in the original software release of Nokia N9. Basically, the device indicated the presence of RFID tags and was able to open the extra levels in the Angry Birds game.
In PR1.1 the device is able to read and write those tags, and any application can now become NFC-capable.
For more information about the technology, and using it in your applications, please refer to the NFC page in developer.nokia.com (the introductory slide set especially is well worth browsing), API documentation in the developer library and the NFC-related sample applications.
Source Nokia Developer