Original poster here - Since the first post in 2010 I've "drank the Kool-Ade" and got an iPhone 4 (non S). The neat thing is the Navionics app still works fine on the Droid with no cell service. I have it for the iPhone too, but take the droid when on a longer trip or in the threat of rain. Its in a zip lock bag and if it drowns or falls overboard -- no big deal.
And I still haven't found a free iPhone equivalent to the great droid app "Currents" that shows the magnitude and direction of currents in the Chesapeake - and predicts them well into the future. Tide charts don't spell it out - there could be a strong southern current through Kent Narrows while the main channel is slack or slightly northern. I use a 2 HP egg beater for an outboard and Bay currents approach the hull speed of my little boat. These things matter to me!