Well, it's not really a ruffle. But, I've been seeing so many of these fun dresses (love the natural waist!) with big ruffle-like collars... they're actually bias spirals sewn on without any gathering. See?
I modified Simplicity 2497, one of my most-used (but not favorite) patterns. I've had fit issues with this one before. I modified it considerably already last fall, turning it into a tunic. Here's the basic look:
That's what I'm calling the collar and armhole ruffles... they're not really ruffles, since they're not gathered, but are instead cut on a sort of eternal bias, cut in a circle. Here's some pics of how I cut them out: