Playing with my new droid phone, I noticed a pdf reader. So from the internet I downloaded a USGS topo map pdf file and used the reader to view it. It works. Sort of. Limited zoom in. It is not georeferenced to the phone GPS system so you still have to know approximately where you are. The plus side is the map is on the phone and you do not need a signal to use it. And the real topo maps have far more detail and accuracy than the cheesy google maps. Downside: Those that have a droid phone already know of the battery problem (my Garmin GPS has 10x the battery life). The map files are large, so watch the space on your card.
A nice gizmo, but I’ll stick to a paper map in a plastic bag.
also try
Google earth for android is nice and MEGL for tracking. Both are free