According to the ComScore report, in spite of its not so glorious start, Apple Maps are the preferred map app for the Apple users. In September 2012, 35 million iPhone owners used already installed Apple Maps. Only 6 million used Google Maps. This number includes iPhone users with older iOS, who could not use Apple Maps.
The reason for the preference is simple: Apple Maps is already installed, so why bother reinstalling Google Maps? Only the more techno-savvy users will actually choose the app that is not provided by Apple. So, it is not the high quality of Apple Maps that cost Google Maps 23 million users in the US alone and probably as many as that elsewhere.
Interestingly, in the case of Pandora, the results were opposite. Since Apple launched iTunes Radio, Pandora got a huge boost in the number of users. One reason is that Pandora was extensively advertised during the launch of iTunes Radio. Pandora smartly responded by eliminating 40-hour per month listening limit. It is very possible that the effects are temporary. As Apple Maps app shows, Apple users rarely go elsewhere for apps they need, if they already have them pre-installed. And as iTunes Radio starts covering more countries, it is very likely that it will be the listening app of choice for most Apple users.