I'm a bit unclear after googling it.... can any of the early iOS5 adopters chime in? Is there going to be turn by turn voice nav implemented in iOS 5? All I can conjure up is that Apple bought the company Siri.
The garmin app doesn't have built in maps. It updates on the fly. Unless you think that the maps are stored in even with the app only being about 10 MB...I look at the built-in maps app as a "technology demonstrator", but the available apps are so much better that I have relegated Maps to my third-page Ignore folder.
I used MotionX GPS Drive for a long time, but when Garmin came out with their app that works just like a Nuvi and has all the maps built-in (so no data connection needed on long trips, and doesn't chew up your data plan) I jumped on that & love it.