I tried using it for navigation yesterday for the 1st time. To begin with, it wouldn't actually start navigating. I entered the address, and it said 'no network available' despite a full signal, and everything else on the phone working. After popping out the battery and restarting, it decided to work. The new interface is nice and clean, and the maps look nice. However, the information at the bottom, including the time to destination, which now changes color based on traffic rather than the old 'stoplight' indicator, were very hard to read in direct sunlight. I also noticed that the map was full of landmarks - everything from stores to cemeteries, and there doesn't seem to be any way to get rid of them, as you could with layers in the older versions.
The biggest issue for me is that I couldn't figure out a way to get an overlay of traffic on the map while navigating, which is the primary view I used in the old version. Living in Boston, avoiding traffic is a constant issue and without being able to see the live traffic on the map, the app becomes a lot less useful. You can go into the route overview and see it, but that's not really feasible while driving. Based on that, I reverted back to the last version until they get this functionality back.