Stephen Few's keynote speech was terrific. It reinforced the importance of understanding human perception. Later that day I went to the Viz Challenge and was so impressed with each of the presentations. Then the judges critiqued them. I was amazed at how accurate they were! I wouldn't have thought any of the viz's needed improvement, but the judges offered great suggestions which were based on principles of visual perception.
So here's the six Gestalt Principles of Perception from Stephen Few's Information Dashboard Design. I highly recommend you get this book, if you don't already have it.