Depends on what you mean by "integration." Google Maps is now a standalone app available (from Google) in the App Store, but it does have quite a different interface from Maps on iOS 5.
I'm not sure how the Google Maps integration works per iOS6 to be honest. All I know is that Google Maps opens whe I click on "view in maps app" in a variety of third party apps I've installed (real estate apps for example). I suspect that should I upgrade to iOS6, those apps would start opening Apple's maps, and I would severely miss the street view. That concern is currently putting me off, and I see no easy way to downgrade back to iOS5 should I'm forced to use Apple's maps app.