Latitude is very likely to succeed because it presents a compelling, simple proposition: “see where your friends are in real time.” It’s also easy to adopt and, as mentioned, built upon large installed bases of existing Google users, in the form of Google Maps for Mobile and Gmail.
Yet the iPhone implementation is curiously "flat." It's currently missing the messaging feature of the Android version, "shout outs," which makes it much more interesting and useful.
In Android, Latitude is integrated directly into the Maps app and there's a map view and a list view, which provides access to IM/Twitter-like updates (shout outs) with those to whom I'm connected. While it's difficult to describe in the abstract, it's essentially mobile IM (a la Google Talk). Thus Latitude becomes a location-based messaging platform, beyond a simple friend finder.
The Google Mobile Blog explains why the iPhone version of Latitude is a Web-based app, rather than a native app for the iPhone:
We worked closely with Apple to bring Latitude to the iPhone in a way Apple thought would be best for iPhone users. After we developed a Latitude application for the iPhone, Apple requested we release Latitude as a web application in order to avoid confusion with Maps on the iPhone, which uses Google to serve maps tiles.
Google, like Apple, continues to push for improvements in web browser functionality. Now that iPhone 3.0 allows Safari to access location, building the Latitude web app was a natural next step. In the future, we will continue to work closely with Apple to deliver useful applications -- some of which will be native apps on the iPhone, such as Earth and YouTube, and some of which will be web apps, like Gmail and Latitude.
Unfortunately, since there is no mechanism for applications to run in the background on iPhone (which applies to browser-based web apps as well), we're not able to provide continuous background location updates in the same way that we can for Latitude users on Android, Blackberry, Symbian and Window Mobile.
As a Web app I'm guessing it can't do messaging, which is why the shout outs/IM functionality doesn't appear.
The paragraphs above from the Google Blog post are strange and interesting. Google is explaining why Latitude may fall short on the iPhone and it's also gently criticizing Apple for deficiencies in the functionality that Latitude is able to deliver:
"Unfortunately, since there is no mechanism for applications to run in the background on iPhone (which applies to browser-based web apps as well), we're not able to provide continuous background location updates . . ."
This line: "After we developed a Latitude application for the iPhone, Apple requested we release Latitude as a web application in order to avoid confusion with Maps on the iPhone, which uses Google to serve maps tiles" is also very interesting. Apple wanted to avoid "confusion." Hmmm . . . Confusion may be a euphemism for something else.
I think Apple wanted to avoid Google totally taking over the the Maps app on the iPhone, one might say "colonizing" it. Even though Maps on the iPhone has Google branding and data, it's not completely Google centric at this stage.
As a consequence of all this Latitude for the iPhone (in its current form at least) will probably fall short of its potential.