Well, these aren't really left overs, but more like perfect souvenirs for birthday parties. I can also see them used at weddings, or other events. It's perfect way to send your guest home, and to keep people like me from sticking my finger in the frosting "just to taste". This is how cupcakes were made to be served, single portion, ready to go!
Photo Credit: +0+cupcakes.com's flickr