as radesix writes you need a metrics framework. In the company I work for we use Google Analytics. It gives a pretty good overview and is very easy to use:
To start it up
// Optional: automatically send uncaught exceptions to Google Analytics.
[GAI sharedInstance].trackUncaughtExceptions = YES;
// Optional: set Google Analytics dispatch interval to e.g. 20 seconds.
[GAI sharedInstance].dispatchInterval = 20;
// Optional: set debug to YES for extra debugging information.
[GAI sharedInstance].debug = YES;
// Create tracker instance.
[[GAI sharedInstance] trackerWithTrackingId:@"YOUR TRACKING ID"];
To track an event:
id<GAITracker> tracker = [[GAI sharedInstance] defaultTracker];
[tracker sendEventWithCategory:@"TITLE" withAction:@"paused" withLabel:@"success" withValue:[NSNumber numberWithInt:5]];
Read more at http://www.google.com/analytics/