The developer of the iOS game "BattleHeart" has announced some notable success with a paid-app port to Android recently[1]. Not at a level of equivalence, but at the level of 'worth doing' [2].

Though that uptake may not translate to a non-game app. Particularly in a niche skewed so heavily toward Apple's base, rather than Google's. And hinging on a component that reviews very well out of the box on the iPhone and as middling on many Android models.

[1] http://mikamobile.blogspot.com/2011/06/android.html

[2] Caveat two: he was using Unity middleware, which greatly lowers the effort of porting.

Yes but BattleHeart is not a top 200 even in iPhone games if I remember the article correctly. Camera+ is Top 10 overall, which based on my experience in the app store means its probably selling at a 100x greater rate than Battleheart. So there is a huge difference in addressable market between the two apps.