I am using C2 to prototype with at the moment, I have been creating commercial casual and indie games in other languages for quite a few years things such as pascal, c#, monkey, objective c to name a few.
It is great to be able to put together a working game in a few hours and see if your idea clicks or not, this is when I would go back to my language of choice and create the game, but as C2 adds more and more features I hope to get to the point where I will just create the game in C2 and never look back, maybe it's because I'm too used to having low level access to many things but when I think of a feature that needs access to lets say the stencil buffer it is quicker for me to do it in c# than hack a way of doing it in C2.
But as I said I love C2 and hope to use it soon for actual games as some of the example projects and works in progress you see on the forums are very inspirational.