I do have the navigation system and am impressed with it's performance so far. I have only had the truck since Saturday but I've used GPS in my vehicle before. The Nissan Navigation system is nicer than what I had because you can plug in your destination on the fly. Everything you need to run the navigation is in the vehicle. I had a GPS unit that could attach to my palm pilot and I had to program each route I wanted to drive into the palm from my PC.
The system in the Titan gives you turn-by-turn directions, which can be voice-guided if you choose. The bird's eye map view is really neat and you can switch to a plan view mode too. One of the coolest features that I have found so far is the ability to program a quick stop while on a currently running route. If your in the car in an unfamiliar area with the family and you need to find an ATM, restaurant, hotel, rest area, etc., you just hit a couple of buttons and the systems gives you the 5 nearest choices, directions to them, and distance.
It appears to be very programmable giving you the ability to avoid certain types of roads that you don't want to be on, different areas of town that you know are normally congested, and stuff like that.
I am in the military and have found GPS really useful after a move to a new area. Especially when looking for housing. Whenever we would see an ad for a house for rent or an apartment complex, we would simply punch in the address and have no problem finding it. The Nissan navigation system will give you the same ability.
In addition to the navigation you have the information center which will give you two trip information screens (time elapsed, distance, and average speed), a gas mileage screen including a bar graph which depicts your real-time mileage (you can see it go up and down as you come on and off the gas pedal), maintenance info, and tire pressure readings.
I'm sure there's a few more features that I haven't gotten too. To sum up, no, it's not the most necessary thing to have. Us guys pride ourselves in being able to find our way around anywhere with only our natural sense of direction. But, if you have the money to spend, I think it's a worthwhile addition. I'm glad I got it. It will certainly help out when we're moving to another part of the country, which we will do quite often.
If you have any more specific questions let me know. I'll be more than happy to help.