Yes, this is hard, due to the black-box nature of the App Store. Can't really measure conversions through it. Android is better for this - I've seen some deve

Yes, this is hard, due to the black-box nature of the App Store. Can't really measure conversions through it. Android is better for this - I've seen some developers release for Android, optimize and test there, and then take their learnings to produce an optimized application for iPhone. In addition to Google Analytics for Mobile, there's a bunch of companies that have free products that allow measurement within iPhone applications and therefore optimization - Flurry, Motally, Mobclix, Medialets, Localytics, etc. I own a chunk of Flurry and think it's the best, but don't take my obviously biased word for it. None of them, including Google Analytics, measure mobile web to mobile app conversions. All of them are potentially affected by Apple's recent terms of service changes for iPhone 4.0. No one knows just how affected. When it comes to promotions, the only area where you can reliably measure is app-to-app advertisements. (And again, who knows if this will be supported in iPhone 4.0.) Right now I know AdMob and Burstly offer conversion tracking if you're advertising through them. Flurry offers a cost-per-acquisition product called AppCircle which I think works quite well, but again, I'm biased. Flurry also has some cross-application tracking (we'll show you how many users on your application A also use application B) but it doesn't quite meet your use case, because it won't show you users who were on application A and touched the ad for application B and then used application B. I don't think any of the other companies mentioned above offer anything better than what Flurry's got - but I'm not certain.