It is no secret here that I am a huge fan of the integration of Google Earth into Civil 3D. For that reason, these cases tend to land on my desk. The use of this data for preliminary planning purposes can save both time and money.
Here is a quick and easy one that may have you scratching your head at first.
If you ever find that your Surface Elevations are off by a considerable amount, make sure to check your insertion scale. The elevations should be in feet, but if you happen to have your insertion scale set to inches, your elevations will be off by a factor of 12.
To change this, type UNITS at the command line. In the Insertion Scale section, change this to feet. Because this only applies to data being inserted, you will need to reinsert your Google Earth Surface to show the corrected information.