I started working on a new app and I wanted to use all of the new iOS5 features (including storyboard) but I\'m afraid to limit my app to iOS5 users only.
I couldn\'
Marco Arment tweeted recently that 92% of his users are on iOS 5.
His last detailed analysis is from november.
Keep in mind that Instapaper (Marco Arment's product) is relatively tech-oriented and it may not be representative of the market you're looking into.