At University I used to do lighting design for theatre (still do occasionally). I put lighting design in the same category as good typography, and the differenc

At University I used to do lighting design for theatre (still do occasionally). I put lighting design in the same category as good typography, and the difference between 100ms and 300ms page load time. After most shows, 90% of the audience couldn't tell you anything about the lighting, but good lighting absolutely lends to the overall experience. The right use of colours and angles in a scene can really add to both the immersion (in the sense that you believe in the setting) and the mood (in the sense that it adds to the tone of the scene). We have data on fast page load times - we know that it makes people more likely to use certain kinds of site. They won't know why though. I am pretty sure that the same is true with font rendering, kerning etc.. Done right it makes for a pleasant reading experience, done wrong (or inconsistently) an unpleasant one, and most people wouldn't be able to say why.