Most of us simmers/gamers probably have a great, bulky, power hungry and overheating graphic card that can handle heavy 3D rendering and plenty of effects. Sadly, the Google Earth plug-in does not make a very good use of all this computing power. While I hope it is going to improve by every release of the plug-in, I would like to give you a small hint that can greatly improve the graphic in the Google plug-in and in GEFS as a consequence.
The only limitation here is your graphic card. If it is high-end enough, you probably have access to some settings via the card's driver. It usually can be found in the display settings of your operating system (in the advanced section). Each manufacturer and/or model of graphic card will present it differently and, there, I would recommend to look on the internet for details about how to set it up.
In the end, what we are looking for is something called anti-aliasing. It is not active by default in the Google Earth plug-in and there is no way to turn it on except for the manual driver settings.
Anti-aliasing, for those who do not know what it is, is an algorithm that smooth all the scaling (jaggies) you can see in an image (http://en.wikipedia.org/wiki/Anti-aliasing).
Most 3D graphic card drivers will offer a way to force this anti-aliasing to be turned on. Usually the default setting is to depend on the application to ask for anti-aliasing. Your driver probably offers an option to make it "always on".
I am talking about anti-aliasing because it is probably the most widely spread option among graphic cards, and also one that has the greater impact on rendering quality. Other settings may be available in you driver configuration panel (such as Anisotropic filtering or Texture quality).
Anisotropic filtering (http://en.wikipedia.org/wiki/Anisotropic_filtering), if available, will also dramatically improve the rendering, especially when flying low and looking far.
Note: I do not own a Mac but from what I could read, it is apparently tricky to force 3D options in Mac OS. If anyone has some advice on that matter, please let me know.