Before you start backup your myplaces.kml by saving manually. In Windows you will need administrator privileges. On OSX or Linux you may need to add sudo before a command if you get permission errors. If your Dropbox or Google Drive etc folder is somewhere non-default, you'll obviously have to change these paths.
Make your new cloud folder and move the .kml there manually or by:
mkdir ~/Dropbox/GoogleEarth
mv ~/Library/Application Support/Google\ Earth/myplaces.kml ~/Dropbox/GoogleEarth/
Make a soft link from your cloud copy to local copy:
cd ~/Library/Application Support/Google\ Earth
ln -s ~/Dropbox/GoogleEarth/myplaces.kml
In terminal replace myplaces.kml with another soft link:
cd ~/Library/Application Support/Google\ Earth
rm myplaces.kml
ln -s ~/Dropbox/GoogleEarth/myplaces.kml
Make your new cloud folder and move the .kml there manually or by:
mkdir ~/Dropbox/GoogleEarth
mv ~/.googleearth/myplaces.kml ~/Dropbox/GoogleEarth/
Make a soft link from your cloud copy to local copy:
cd ~/.googleearth
ln -s ~/Dropbox/GoogleEarth/myplaces.kml
In terminal replace myplaces.kml with another soft link:
cd ~/.googleearth
rm myplaces.kml
ln -s ~/Dropbox/GoogleEarth/myplaces.kml
'My Places' is stored at C:\Users%username%\AppData\LocalLow\Google\GoogleEarth\myplaces.kml. You usually can't navigate to the AppData folder without typing it in the path bar.
Copy this .kml to a folder on Dropbox or wherever on the cloud. Get the full path to this folder (eg C:\Users\Malcolm\Dropbox\GoogleEarth).
Now edit the registry key:
- click Start
- click Run
- type regedit and hit enter
- modify the string for HKEY_CURRENT_USER\Software\Google\Google Earth Pro\KMLPath to the path of your cloud copy
To sync with first machine on Windows "just" modify the registry key to the path of your cloud copy. Good luck.
With thanks in part to WBond and GEarthBlog