If you are having trouble with your faceplate sitting flush, you might be using the wrong holes on the side of your unit to mount your brackets.
I had mine like this:
I just couldn't get my dash trim piece to snap in. I trimed a tiny bit off the front edge of my brackets and I managed to get the bracket to move forward a notch.
My dash piece went on perfectly!
I'm really happy with the unit so far! All I have left to get working is the aux jack and thanks to the handy chart that Deathalo posted I don't think that is going to be too bad. Thanks for all the wonderful tips guys.