When it comes to doing earthwork volume calculations Autodesk Civil 3D 2005 makes the entire process very streamlined.
The process boils down to initiating the "ReportSurfaceVolume" command, from one of the various methods, then telling the software I wish to do a new calculation. Lastly, I select the two surfaces that I wish to compare. The Panarama window instantly provides the results. These results include the "Cut", "Fill", and "Net".
The software uses the composite method for the calculations. Civil 3D Help explains this method as "...using the points from both surfaces, as well as any location where the triangle edges between the two surfaces cross. The new composite surface elevations are calculated based on the difference between the elevations of the two surfaces."