The lollipops really don't look like lollipops... Also, make the cupcake more dimensional; take advantage of the simulated processes Threadless can print now.
Err, I can't really think of any other advice, so good luck.
like the concept. I'd lose the cherry on top and the sprinkles on the cheek bones - and I'd try and make it look a little more 3-dimensional. The suckers in the back for the cross-bones look particularly flat, I'd try and bend those lines to make it look like they're really printed onto a sheet of cellophane that's been wrapped around a round sucker. I think making the lines on the bottom half of the cupcake a little thicker (not necessarily darker) would make the skull more obvious