My wife has a 2003 Acura MDX with Nav which I like because of simplicity and accuracy. So I decided to add Nav to my Prius. I am totally unimpressed with Toyota Navigation.

Compare to Acura/Honda, Toyota nav is inaccurate and unreliable. Simply a terrible navigation compare to Honda/Acura.
For example, Toyota misses my home and work by a block. Often it gives me a wrong direction. On the other hand, Acura is right on the dot. Usually +/- a few feet. Toyota is +/- by a block or more. I can trust Acura system 90% of the time. On the other hand, I don't trust Toyota nav 50% of the time.
In Acura, when nav gives the directions, stereo goes silent and then comes back on after, so that I can hear the directions. Toyota doesn't do that. In Prius, you have to turn off the stereo or keep it low so that you can hear the directions. Waste of JBL option. Toyota doesn't give you option to change the male to female voice.
Programming and use of Nav is much simpler in Acura. Toyota is way too complicated to use for average people. My in-law who has 04 Lexus LS, which has the same nav as Prius, just cannot figure out how to use the nav. No wonder, it won't let you program while driving. You could get into an accident with Toyota nav, if you try to program while driving.
Toyota is pretty much all touch screen system. So your nav screen is full of finger prints. Acura uses the joy stick and touch screen. It is much easier to move around the map with joy stick.
Acura voice command is easy to use and work most of the time. Toyota doesn't work most of the time. I just gave up using the voice command all together.
Acura has much better graphic and easy to read. Whoever designed Toyota nav has color selection problem. It is very difficult to distinguish between the surface road (green) vs. routed road (light blue). Acura graphic is must higher resolution and clear.
Rumor is that Toyota is going to come out with fix. I am not sure we 04 folks will get the fix or not.
In summary, Toyota nav is a waste of money. They need to look at Honda/Acura nav and learn or copy Honda.
Other than nav, I love my Prius. My wife is so envious about SS/SE and steering wheel controls.
