If you see flickering in the display of your model (in Earth or Sketchup), you're experiencing Z-Fighting. Z-Fighting is a sign of excess geometry, too many shapes and angles. Z-Fighting can be eliminated by deleting excess faces. Z-fighting is mostly caused by two faces, situated in exactly the same space. This way, Sketchup doesn't know which face to show, and you get flickering textures.
In Google Sketchup 6, lines didn't intersect automatically yet. Using SU 6, when you draw two faces overlapping eachother, the edges which border eachface don't intersect, which causes two faces to be in the same spot. In SU 7, This issue has been resolved by making edges automatically intersect and create endpoints. The isseu Z-Fighting still remains, because if one of the faces is grouped with other geometry, the edges don't intersect, but the faces are still in the ame place - Z-Fighting.
The "Z" in Z-Fighting refers to the front to back Z axis in modeling, and the visual display stacking order in rendering.
Z-Fighting between a group and a single face