Like others have mentioned, you can hold a Dualshock in one hand and the Move controller in the other instead of using the Nav. But that looks hella uncomfortable. LOL
I picked up my first Move, Nav, and Sharpshooter a while back during a super cheap sale. I'd never tried motion controls before (no Wii or 360). On a game like Killzone 3, that setup is sick. So much cooler than using the DS. So yeah, not a lot of games use it, but the Move is way more accurate than the Wii or Kinect (I've tried both now), and being able to move in 3 dimensions (unlike the Wii) is extraordinary. Meleeing somebody in KZ3 by jabbing your gun at them never gets old. LOL
Since I believe the best use of the Nav is with a full Sharpshooter setup, I'll also mention that the Move locks into the Sharpshooter via its USB port. Unlike guns for other systems, where pressing the trigger causes a physical linkage to shift and poke the controller, the Sharpshooter inputs are instantaneous and 100% accurate. Makes all the difference in the world. The Nav doesn't hook up the same way, but it doesn't matter because you keep your hand on it the whole time and press the buttons directly (nothing is covered up by the gun shell).