right - to start with go to the flashforge section - basically they are all replicator dual clones and that's where most of the basic info threads are :-)

First thing to try is change the software. If you are using replicator-g - try makerware desktop:
http://3dprintboard.com/showthread.p...-x86-computers

The cube dimensions are actually pretty good. bear in mind that at those tolearances just applying a little more pressure on your calipers will make a lot of difference.
Also filament type and make, print temperature and print speed will effect final sizes as well.

Abs won't size as easily as pla. And cheap pla won't size as easily as good pla.
Desktop 3d printing is as much an art as a science.
If your model prints too short - make it longer. It's often that simple.