Google Maps for iPhone has been downloaded for more than 10 million times within 48 hours after its launch. I think this is expected as you can see the quality in the release.
The news was mentioned by Jeff Huber over Google+ congratulating the Google Maps team for the success.
Actually, what is ironical is that I think the Google Maps on iOS is better than the Android (Ice Cream Sandwich) ones at this moment. I did a demo and I really like the app. Congrats to the Google team.