Did you know that your camera has a life expectancy which depends on how many times the shutter was released? Most Nikon models are rated for 150.000 shutter releases (D3 series are rated for 300.000 releases). Once you reach this limit you should either buy a new camera or replace the shutter.
There is an easy way to view how many images you shot so far:
1. Download and install Opanda IExif (the free version displays only JPEG files, but this not a problem since you can convert your NEF files to JPEGs by using your ACR).
2. Open the latest image created by your camera with Opanda IExif.
3. Scroll down until you see “Total number of shutter releases”.
This is your latest shutter count value!