I believe the most powerful aspect of Google Maps is allowing students to create their own custom maps.
Community Review for Google Maps
My Take
I have found that students retain and enjoy geography more when they interact with it. Just merely studying a map on a piece of paper doesn't engage students. Google Map allows individuals to add text, an image, a link - even embed a video for any location on earth. The maps can also be shared - just as other Google applications - with others and groups of people can collaborate on a map.
How I Use It
This year I am having students add geographic locations with each unit of our American history course to a custom map. Students will add locations to their map as the year progresses and at the end of the year they will have a single map with all of the historical locations we discussed marked with links, photos and videos.