I got confused after trying it, because I kept thinking on the first screen that I was using it, while in fact I wasn't: I was supposed to be clicking on Next. I'm not sure what would be best, but I think I want to not go through the four screens that show me how to use it.
I wish the "Save" button was closer to "Add Item" so I don't have to move the mouse.
I don't know why would one use it (why on earth would I want to share a list?), but it is a very well done thing.
Maybe this great interface could be used to power: public forms, enterprise data, a CMS like http://contentful.com/, a general purpose customizable CRUD app for small businesses.
Found a bug: URL custom field type wasn't saving.
Also, grabbing images from a URL rather than download/upload would be a nice feature. Perhaps even grabbing an image from the URL field like a facebook or twitter share does.
Feedback is appreciated!