I like the age-old motif of hearts and keys. It never goes out of style and always seems so genuine and proper. I also like gags involving swallowing a key like in "Arrested Development" so with these cupcakes I'm all set.
So much cupcake decorating is based on the notion of piling heaps of stuff on top of the cake, it's refreshing to see someone make use of negative space here, so to speak. A creamy pool of frosting in the middle of the cake is a nice change!