Google has added the +1 button for Google Maps. If you find a custom map that you really like you can now share it with your friends by clicking the +1 button. By clicking the +1 button you are also helping to rate and promote the custom map.
You can find the +1 button underneath the map description on custom maps. Any custom maps that you have created yourself or that you have found and saved can be viewed by clicking the 'My places' tab.