I had an IstD and now a K10D. When I leave my apartment, my camera is over my shoulder. I assumed the LCD screen on the IstD would not scratch. It simply hung around my neck and brushed against cotton shirts. And, I didn't notice any scratching.
Then I got my K10D and gave my IstD to my sister. Her first comment was, "Wow, the LCD is sure scratched." I looked at it and it was. It didn't render it useless, or even that noticeable, but it was certainly scratched. I'm assuming that bits of grit would blow onto my shirt, or the LCD, and then scratch as it moved against my shirt.
So, I bought some of the plastic PDA protectors and cut them to fit. They worked, after I learned how to put them on, but I usually had some bubbles and they didn't last long. Sometimes one would come loose rubbing against my shirt.
So, I ordered the Aegis. It's dandy. It doesn't do anything active. Just sits there. But, it's easy to clean, doesn't scratch, doesn't interfere in any way. It works.