Attention Mickey and Pirate! I dont know if you have purchased Bluecharts yet, but I have just installed Topo Australia (it has only become available on DVD this week). If you are only going to get one, I think the Topo may be better value. It lacks a few things, like depth contours, tide stations and navigation markers, but it is a comprehensive topographic map of Australia, including all city streets and the stuff you normally get in City Navigator. Its mapping of the shores of waterways is excellent and that's the main thing you need anyway. Here is a screenshot of the Bairnsdale / Gipplsand lakes area in Bluecharts:
and here is the same area in Topo Australia:
Topo Australia is $199, same as Bluecharts, but you only get one license, instead of two, so it is effectively twice as much, if you were planning to share Bluecharts.
Anyway, just thought you should know