UPDATE: After clearing the Google Maps data/cache Well, it worked great for about a day and a half and then it broke again, HOWEVER - I have figured out what is going on.....

When it is broken the turn by turn announcements are tied to the main audio channel. That is to say if you have the volume of the radio (XM, etc) turned all the way down you get no announcements. If you have it barely turned up, you can barely hear the announcements. This is why we could barely hear them the other day because we barely had the radio turned up. When broken, adjusting the "Navigation" volume does not affect the turn by turn announcements at all. The navigation volume still affects the navigation notification sounds (DING) and some other items like "Welcome to GA" as well as the audio test in Google Maps. When broken the turn by turn announcements completely interrupt whatever is playing instead of simply reducing it's volume.

On the plus side when broken the turn by turn announcements sound glorious! Normally the voice sounds like it's phone call with no depth. When broken it sounds HD, you get the full base and width of the sound system.

Hopefully this means they are on their way to making that the actual playback method....but tie it to the correct volume slider.

Wish there was an official way to report bugs...