For those that are wonder where their CG will end up, take a look at
http://www.chiefdelphi.com/media/papers/2048
It allows both weight budgeting and CG estimation. You can use this to get an estimate before the CAD modeling gets too far along. 10-20 minutes spent now on budgeting can save hours (or even days) of rework.
I apologize that the user interface is not slicker and am open to suggestions for improvement.