I have tried my phone on it too and I have the same problem of people not hearing me well. But we both have Blackberry Curves, and from the comments here it sounds like it might be our phones.
I first thought about whether or not GM has the mic in a weird spot, b/c it looks like it is to the right of the steering wheel column behind a small vent in the dash. That's a funny spot, b/c the sound could be blocked from the steering wheel, plus it's a good distance from your head while driving. However, when setting up the bluetooth, it gives you an option to record the name of the phone. Upon playback of this recorded name, it comes through very loud and clear -- so no problem with mic placement.
Now I wonder if my Blackberry's background noise cancellation feature is interfering with the bluetooth system. Has anyone experienced this? I'll try to shut off that feature after the wife gets back with the Traverse. Thanks everyone for the replies.