Dan Peterson posted a nice article about research that is being conducted at McGill University into the exact mechanics that go into a perfect wrist shot. The objective of the research really is to understand the exact techniques and factors that make up a more accurate shot.
The article does mention one difference between pros and novices when it comes to shooting at the upper corners. The difference is that the pros pull the puck in closer to their body prior to the shot to get better control. The research is ongoing and they hope to achieve results that will translate into specific instructions to improve the wrist shots of every hockey player.
You can read all of the article at the Live Science site here.