Apple have rejected a Commodore 64 emulator for the iPhone from making an appearance on the App Store. Curiously, licensing issues are not the problem here; the developers actually signed a contract with the license holders for the platform to make sure there were no legal issues in that department. Instead, the application has been rejected because of this part of the Apple SDK license agreement:
"No interpreted code may be downloaded and used in an Application except for code that is interpreted and run by Apple's Published APIs and builtin interpreter(s). An Application may not itself install or launch other executable code by any means, including without limitation through the use of a plug-in architecture, calling other frameworks, other APIs or otherwise."