With the release of iOS 5 today, there has been some debate at my organization of which OS version we should build for in future iOS apps, iOS 4 or iOS 5. Building to accommodate multiple OS versions is more time consuming which translates to greater costs, and is not always an option. In general, we lean towards the safe side and build to accommodate more users by building for an older OS. However, this also limits what new APIs we make use of in development.
