I would recommend a "report bug/suggest" feature. Because when I dragged a Flickr image to the folder all I got was a header text on a white background (I think the picture has some restrictions for sharing...). It would be insightful to get these details from your end users. PS: I like the intro tutorial. PPS: I hated that I have to give permissions to post publicly to Facebook, or else the sign up process does not go through