most PDA phones have no problem at all with turn by turn GPS. Owning an ATT tilt, i use my phones GPS all the time for turn by turn and it is very accurate.
A car charger solves all the problems of battery drainage. Yes, it takes about 25-30% of my battery per hour using GPS, but with a car changer my battery doesnt go down at all. To people who walk with their GPS...well it cant be perfect, you'll just have to live with the bad battery life or get a dedicated unit.
I am very content with the GPS in my phone and will use all the time as long as i have this phone. If Apple cannot implement a GPS as well as all the other windows mobile PDA phones or symbian phones then i guess they are doing something wrong.