I just bought the app (out of curiosity, I already own Navigon).
It's the European version.
To quick answer the question, all ask about: The music does NOT fade out when the app is speaking.
Here's a quick list of good and bad points:
+) The keyboard is somewhat cool as if you type in names, only letters available are pressable on the keyboard. This speeds up entering addresses.
+) 4 calculations for routes: Fast, Short, Economic and Easy. Navigon uses Fast, Short, Optimal (whatever that means) and Beatyful
+) iGO seams to youse the Accelerometers. If I use the app inside my house, the No-Sat-Link icons is shown. But if I move around in the room, it disapears!
+) You can use different icons for your representation on the map.
-) Voice quality is bad.
-) Overall you need more buttons pressed to start navigation
-) If you exit the app during navigation and enter back in, it doesn't automaticly continue.
-) The map seams somewhat colorful and overloaded.
-) No RealView kind of thingy
-) No Text-To-Speach. This is only possible with synthetic voices of which none is included.