BMW has this too... on all models from what I can tell on the car forums. I have a 5 series and it all works great, but I get a slight echo.
The echo goes softer to almost not audible if I turn up the volume ON THE PHONE while talking on it via bluetooth.
My address book synchs and all other things seem fine. The callers on the other end say it sounds great too, so I have just learned to live with it and remember to turn up my phone when I hear it.