The other day, a friend of mine and I were plotting to take over the world when one of us suddenly had the need to diagram something. I have a whiteboard in my closet which I've been meaning to hang for the last 9 months, but the problem is that I never think to hang it when I don't need it, and when I do need it, I don't want to stop what I'm doing long enough to hang it. My friend had the idea of using the whiteboard marker directly on the mirrored doors of the closet in my office. I never liked those doors, so I figured the worst that could happen is that we would ruin them, and then I could replace them. We discovered, however, that mirrors make great whiteboards, and both doors have been covered with diagrams and various scribbles ever since. It turns out I had two huge, almost floor-to-ceiling whiteboards sitting right behind me all this time.