I posted this on another thread but thought it would ok to post here as well....
i have poked around at some of the apps out there (i have a droid) and as neat as some of them are its the battery life that will let you down. they need to have a battery on the smart phones that last at least 12 hrs with the GPS/phone etc running.
that being said I really like the TOPO maps (backcountry navigator) that are available with tracking. with the airplane mode on i hope to be able go full 6-8 hrs with the just the gps and maps running. i normally hunt the county up in maine where you can walk for forever and not see anything/anyone. gps/topo maps on the phones are a huge plus without having to buy another handheld GPS unit.