Personally, I'd never own another vehicle without a NAV system.  Even my
motorcycles have one.

The only bug I find in the Prius unit is that the voice recognition doesn't
work all that well.

You say "Potato."
It says "Tomato."   >:o(

Other than that, it's fine.  It detours well, especially unfamiliar
neighborhood streets, and gets me to unknown destinations fine.  The
addition of the NAV package allows for the no-hands cell phone too.  Should
it become law (no hands on the cell), it will free you of a Bluetooth
headset and dialing since it's built into the display as well.  Better
stereo too.

Besides, it makes the car geeky and serves to impress everyone around you.

B~

I don't know anything about the '06 models having anything different
than previous ones, but as an owner of an '04 I have no idea why based
on that you wouldn't want to have it.  Now, I haven't ever used a
navigation system in any other car, so I have nothing to compare it to,
but I use the one I have all the time and absolutely love it.  On those
occasions when I'm driving a different car, I feel lost (literally)
without it.