The NEF format is, as you suspected, simply RAW data that the CCD has captured. It has not been modified in any way by image processing software, either in-camera, or off-camera. It is not a usable format for things like printing. It can be viewed in Nikon View 5.0, or Nikon Capture. Most people that use the NEF (RAW) format are ready and willing to do some post processing in software like Photoshop. The NEF format is the closest thing to a negative or slide that a digital camera can make. It is pure raw unprocessed 12-bit image data with no manipulations of any kind.
Any format that moves away from RAW (NEF) format is throwing away data.
The TIFF format is an 8-bit format that comes from that same RAW 12-bit data. It is 1.5 times larger than NEF, but contains less image data. In the case of TIFF, the conversion from 12-bit to 8-bit crams 12-bits of data into 8-bits of data space. That is no big deal, since there are no devices that I know of to display the full 12-bits of data anyway. Even the monitors we use can only display 8-bits, so you never really see the full 12-bits. So, if I were going to use a format for printing to photo paper, it would be TIFF. It is a loss-less format in that, once the 12-bit to 8-bit conversion is done, there is no more data loss. You can modify and save the image many times with no data loss, since no data compression is taking place. (like with the JPEG) format. The TIFF format is a widely used loss-less format. The only real drawback is that it is HUGH. A 9.5MB RAW file will convert to a 17.6MB TIFF file. A one-gigabyte IBM Microdrive will only hold 54 full res TIFF files.
I use RAW (NEF) format extensively, since I want ALL of my original data to be there when I decide to work with an image. JPEG throws away an enormous amount of data. TIFF throws away some too. So, wouldn't it be better to shoot and store your images in NEF. Then when you want to do something with the image in the future, you can simply make a TIFF or JPEG out of it. You will, like a negative, always have your original pure data to work with. Maybe someday we will have 12-bit imaging devices to work with. When that day comes, your images will be much better than the images many chose to convert permanentley to 8-bit.