GPS on my EVO sucks sacks, if my phone's 100% charged when I get into my car, and I hook it directly to my car charger the GPS will kill the battery faster than the charger can charge it. So if I needed the GPS to be constantly on for a long trip I'd be SOL. I dunno if the iPhone has this problem too, but I know my clunky ass Magellan doesn't
therefore stand alone GPS >>> phone GPS
That sounds like more the screen is at too high a brightness. When I had my Incredible, putting the brightness at max the charger couldn't keep up, setting it to medium it would stay at 100% charge with screen on and google nav.
Google nav has always worked great for me. Love that time this semi driver walked up to me with his iphone in hand and asked me if I knew where ____ was, showing me an email with an address. Typed it into my phone, and showed him where to go.
I drive multiple company and personal vehicles, a stand alone gps would suck ass. My phone is always on me and has never let me down. Lots of times I don't even know the place I'm going, use google to find it, hold down the address and bring up google nav, usually brings up the phone number too to make sure they're still open. Good to go.