It's not terribly difficult to integrate Google Maps into a FileMaker solution using the WebViewer, and many FileMaker developers have certainly done just that. But there is a lot more that can be done, and a lot that can be improved. Delfs Engineering has solutions for Google Maps/FileMaker integrations.
One issue is the number of calls to Google Maps. Google intends for people to manipulate data on a map inside a browser window. If instead you are using a native FileMaker web viewer window you are actually reloading the map with every change you push from FileMaker. This means impaired performance, and also racking up more page loads with Google (and that can get costly). Delfs Engineering has a novel approach that allows FileMaker to interact with a Google Map without reloading it.
The other issue is getting data the other way – from Google Maps back into FileMaker. For example – a FileMaker solution that involves delivery route optimization. It sends destination data into Google Maps, which then optimizes the route, displays directions, times, etc,
Getting this information back into FileMaker is very desirable (you could recorded the records based on the route optimization) but also very difficult.
Again Delfs has a solution that works, and can be added to your database through their FileMaker development/consulting service.