I recently released Starting 11, an iPhone app in which you can pick your own football team line up and share it via e-mail and Facebook.
From idea to app store submission took about 10 evenings of work. The lions share of that time was spent perfecting the user interface. Below are the design iterations from idea to App Store release, click the images for full versions.
Since I had the idea for this app just before the FIFA World Cup started, I quickly decided to use the Xcode template "Navigation-based Application" to simplify development, hoping to get it published before the World Cup had finished. By focusing on polishing the pitch view, which would be the view where the user spends most of his time, I figured I would get the most bang for my efforts.
Initial idea sketch