All you GUI programmers (or non-programmer vision/perception geeks) should run over and take a look at Evaluating Low Spatial Frequency Compositions at Boxes and Arrows. It'll show you new ways of thinking about icon design.

My theory of icon design is basically "Ugh. I can't draw at all. I hate this," so I'm not sure learning how to tell which visual pathway my icon designs are tickling is the kind of lesson I need. But, nonetheless, it's interesting stuff.