There are a lot of options for Nav on the iPhone. Mapquest is a good free option. This is a double edged sword for Android. The stock Map app is "good enough" to kill the market for premium Nav apps.
blocked on most handsets/carriers on stock ROM so rooting is required. JB your iPhone to get the same functionality.
Regarding these two points, it was announced yesterday that offline caching of maps is going to be added to the Google Maps app on Android which makes it at parity with most (it not all) GPS apps. The update for that is due in a few days.
The Wifi hotspot feature is a stock Android 2.2/2.3 and will not be blocked at all on the Nexus S (just as it isn't blocked on the nexus one) so it will never be a requirement to root for Wifi tethering on either of the nexus phones.
Of course carriers block or charge for the feature on carrier locked/branded phones but the Nexus S isn't in any way modified by any carrier.