I always thought of modals in modals as an example of poor UX. I though that if you have information that belongs in a modal, you shouldn't have information that requires an additional modal. I believed the modal should be the final point of distance away from the "main UI".
Now I'm not so sure. I came across a well implemented modal-in-modal interaction and it felt quite natural (in cushionapp).
What does everyone think about having modals within modals?