The only command i find useful is "suspend guidance".
It's useful when you're using the navigation to guide you somewhere. When you get to a point that you recognize, you can tell it to "suspend guidance" and the thing stops talking to you. It's easier than having to press all the buttons on the screen to stop the guidance. You can also tell it to 'resume guidance' and it will start guiding you again.
Other things the voice rec. can recognize: (per my memory)
"FM radio" -switches whatever mode you're in to FM
"Radio OFF" - turns the radio off OR
you could just press the buttons on the steering wheel... lol
You can also use the voice rec. to call a certain phone number by reading off each digit (if you have bluetooth set-up) but it can't recognize the names you've programmed the numbers as...
And you can tell it to "GO HOME" if you have your home address programmed in the nav. That is, if it decides to understand you. A lot of times you give it a command, and it'll tell you "point of interest not found" or something like that... Then it changes the nav screen view and inserts all these symbols... honestly it just makes more work for you
Other than that, i don't find it useful.
Commands i wish it could understand:
-Temperature increase/decrease to (whatever degree)
-Fan speed increase (or decrease)
-air conditioning OFF (or ON)
-defroster ON (or OFF)
But check out an Acura and it has them...