For me a killer problem is that it doesn't have access to the massive Google Local place database, so I find myself unable to find the addresses of things I want directions to (making the question of whether I'd get good directions to the destination pointless).

Here are screenshots of an example situation I ran into yesterday, while trying to pick up my iPhone 5 from the UPS Customer Center:

http://cache.saurik.com/tinyimg/ios6upsmap.png