Protected map layers, a part of the Google Maps API Premier package, allow you to create a data table in Google Fusion Tables and keep that table private. Maps API Free allows you to use only tables marked Public. Protected map layers are rendered as clickable rasters. You still have to be careful what data you put into the infowindow, make sure it's only what you want public.
Of course, Maps API Premier also allows you to make maps that are password protected, so this will be really useful for enterprises that want to keep their data entirely private but still take advantage of the performance improvements and spatial queries that are allowed by using a FusionTableLayer.