This may sound absurd but bare with me. I have a custom post type. Lets just say "Events" for this example. I want to be able to add events while I'm editing a Page. The reason for this is sometimes clients aren't the most savvy. So by simplifying the places they have to go to edit content helps. Not to mention it would speed up editing when there's a lot of pages/"events".
It could be in a lightbox/model window or fields directly on a page. I'm currently working on a method to just load the Add "Event" page into an iframe. But I don't like using iframes if I don't have to.