Does anybody have experience in cloning an app/game from the iphone?

Don't get me wrong I never saw a single line of code from the regarding app or steal any picture/texture - it was real work to develop the app . So I mean of course, it is in some way 'stealing' the idea if one writes a clone on a different platform.

Anyway ... does anybody have experience in such a situation? are there copyright problems?

does it make any difference if I sell my app or publish it free?

thanks for your time!