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Curious, what NAV system do you use? I use a Pioneer AVIC-D3 (looking to get the Z2 though) and it greys out the address input option while the vehicle is in motion.
OEM Navi in Lexus does the same, but it is overridable if you know the secret handshake. You also have to hit a stupid 'I agree to drive not quite like a moron to turn it on.'
OEM Navi in MB lets you enter at any time and doesn't bother you with silly 'I agree' crap...but it's a far inferior Navi unit in operation than the Lexus.
I think a click wheel might be a substantial improvement (speed wise) to scrolling through lists of cities, streets, etc, than entering though a touch type (Lexus) or joystick type (MB) system where you spell out the city/street and the Navi pares down the list based on the letters entered. One would have to play with it to know for sure, but I think the possibility is pretty strong.
 
OEM Navi in Lexus does the same, but it is overridable if you know the secret handshake. You also have to hit a stupid 'I agree to drive not quite like a moron to turn it on.'

Which is funny - because I've always thought that there was some driving test where you *had* to drive like a moron in order to buy a Lexus.

When I grew up I thought (based on observations) that there was some kind of driving test that people had to fail in order to buy a Cadillac.

Today, those people drive a Toyota with added eye-candy called a "Lexus".
 
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