When I am out to demo, I have two things in mind: I like to feel how the ski works for me personally, but I also like to figure out why that is and how it might work for others. I am clear that I have a lot to learn in my skiing, and my skiing is going to change over the course of a season, so it's important to me that I get as objective in my assessment of the skis as I can be. I also plan to post reviews here, so my goal is to be as helpful to as broad a range of others as I can be.
So, I take notes. A voice recorder is a good idea, but I haven't ever tried that. When I demo, I play with extremes of technique (banking v. angulation, fore/aft moves v centered, riding the edge v steering, etc.) and stick to terrain that is "comfortable". I admit that last year when we were skiing in fresh snow, I broke some of these "rules"!
I find that knowing I am going to write the demos for Epic that I get more analytical, and that helps my personal analysis, too.
I do look for the smile, though. At the end of the day, that's what really matters.