I frequently use Google maps to find places. Most of my research is in the areas that used to be the old (US) Northwest territories. While the grid surveying system established then, is still being used, it is sometime difficult to determine where places existed on new maps. By using Google Maps, current plat maps and the old plat maps, you can locate ancestor's farm precisely.
As a working tool I find the original locations as stated above, then mark it on the Google maps with the pins to know where my ancestors lived. The pin is identified with name and date. I also color code the pin to family.
This gives me all of the location for all time periods on one map. For short term (The life of Google) I periodically backup the files; myplaces.backup.kml and myplaces.kml. (PC: C:\Documents and Settings\user\Application Data\Google\GoogleEarth) you can also move the pins to other computers by copying these files to the same folder on that computer.
For long term, I do a screen copy of the Google map and save it to the disk.