The iPhone doesn't have these problems when using fuller-featured 3rd party apps either.

Anyone with any legitimate navigation need gets a third party app with offline maps, like the above mentioned Navigon, which supports all your mentioned features and more, such as live traffic based re-routing (which works extremely well) and the full Zagat guide for finding nearest decent food.

While running a full blown GPS app, talking on a conference call with Bluetooth, and using live traffic so the data connection is running as well, the iPhone 4 gains about 1% charge per minute with a 2 AMP charger.