Yes, I find it interesting to note the different types of errors. There are some random errors, but many of the errors seem to be repeated. It looks like a lot of people ended up in the wrong code path, resulting in blue/white pixels in the lower half, while fewer people made the reverse mistake (yellow pixels in the upper half). There are a lot of purple pixels in the upper right; I wonder what led many people to the same mistake.

Another interesting thing is to try to reverse-engineer the worksheet: section B is the sphere, section C is the ground, and section D is the sky. But then there's the lighting model, shadow, etc.