Google City Tours, the service that generates walking tours for important cities, has a new feature that lets you import custom maps. After logging to a Google Account, you can go to the importing page and select one of your maps.
The service would more useful if you could customize a tour by reordering sights and defining constraints. Other features that seems to be missing: saving tours, sharing and printing tours.
Google City Tours will probably become a feature of Google Maps that will help you find more about a city and plan your trips.