Read the comments on the Flyer Forum about this, and one of the concerns was lack of airspace data. Having had a quick look at the Google Maps API pages, is it not possible to include some airspace markings on the map from an xml file? I guess the limitations are on what sort of shape primitives the google maps API supports?
That said, excellent looking tool. I reckon the map interface is a good idea if used in conjunction with a proper paper chart..