To export your Google Maps starred locations:
Go to Google Bookmarks: https://www.google.com/bookmarks/
On the bottom left, click "Export bookmarks": https://www.google.com/bookmarks/bookmarks.html?hl=en
After downloading the html file, run this script on it to generate a KML.
It's hacky and doesn't work on all of them, but it kinda works.
Google has now provided their own tool to export your Map data in JSON format at Google Takeout