Mine works great when it works at all...
About 50% of the time it works as expected, and is pretty much spot on for destination names (has some trouble with names when calling people in my address book, but is generally close enough that it calls the correct person or at least shows a list of potential contacts with the correct one in it).
The other 50% of the time it's almost like the microphone doesn't even turn on. The voice card pops up and appears to be listening but nothing I say is registered. Sometimes it will start to work again on its own after several tries, and sometimes I need to restart before it works again. I was assuming it was a software bug introduced in a recent release since it worked flawlessly when I first got the car but I've had two updates since it broke and the problem still appears. Probably time to schedule a SC appointment.