I'm having issues with google app too. I love how I could do a voice search for a restaurant, store, address and have the result show up with options for getting directions or show on map or call the number listed.
But lately nothing happens if I tap 'get directions'. The button will flash, so its registering the tap, but it fails to open the map app. Its like this on my wifes phone as well. I've tried restoring, updating, uninstalling google app and reinstalling and nothing works. This is a huge part of my iphone usage so this really bums me out.
By the way I'm a iphone 4 on 4.2 and my wife is a 3gs on 4.0
Anyone who reads this please let me know if this is happening for you as well. Also I used to be jailbroke but i'm not atm.