Google recently posted at the SketchUp blog about new features in SketchUp 7 that help improve buildings 3D models for Google Earth. The new features help improve the textures for 3D models allowing you to separate each side of a building in the textures so you can re-touch the photos removing obstructions (trees or cars) which block the sides of the building in the photos.
Here is the start of the process using the original photo:
And here is the final result:
Google has a number of useful video tutorials for making models for Google Earth with Sketchup. If you are looking for some real training for SketchUp, the best resource I know is the Google-authorized training company “school“. They have some online training webcasts here, you can also purchase some training DVDs, or attend one of the live training classes in locations in the US.