I created a Cocos2d-iphone game for the iPhone/Sphero in 36 hours.
When I got a Sphero from the Seattle Startup Weekend in May, I brainstormed what this thing could do. I thought of a cool behavior for a Sphero, where it changes its color as it moves based on a picture of your choosing. Friday, it clicked: turn it into a picture guessing game similar to Pictionary. The deadline was midnight Sunday, so I had to act quick. I bought my snacks and settled into a 36-hour marathon programming session.
Long story short, I did it. I wasn't so sure near the end, but everything clicked and I even had time to prepare my other project for the competition.