I'm having severe trouble with Google "My Maps" (server won't save, polygon attributes changing sporadically, etc). So now I'm trying to work in Google Earth (saving files as I go) and sync with "My Maps" later. However, not only am I having issues with the saved files, but I can find no documentation on syncing my local polygons, etc with "My Maps". Would someone mind pointing me in the right direction for this kind of usage? Is this even possible? If push comes to shove I'm more than happy working strictly in Google Maps, but I need a reliable local saving paradigm as well.
When editing a My Map on Google Maps, there is an "Import" link next to the "Collaborate" link.
This import allows you to upload the KML/KMZ file you saved in Google Earth. (Via "Save as...")
Import KML dialog box details:
Import KML
Add map data from a KML, KMZ, or GeoRSS file to this map. This may take a few minutes depending on the speed of your internet connection.
Maximum size: 10MB
Mentioned at the bottom of this support article, too: