While Google Maps on smartphones is great, it's no replacement for a standalone turn-by-turn navigator, as it doesn't work when you lose a signal. But that may not be the case for long.
Apparently, Google may be offering up a version of Navigation that uses cached maps in your mobile device to work just fine even when you lose a cell signal. It's kind of a nice middleground between what they're offering up now and making you download a huge maps file of every street in America. Of course, this is just a rumor, so we'll see if it actually becomes reality.