For me, when something loads too fast, I think something broke because my brain has been wired to learn than actions through a web browser are generally not instantaneous and take a bit of time. Even if it's just a fraction of a second.

I really like this idea, but for some reason I think my brain would be more comfortable with a ajax spinner appearing for 300ms rather than an instant page load. For instance, I built something recently which loaded images on a page via ajax calls. It happened very quickly, 50ms maybe. The loading seemed way too fast so I actually delayed the images by about 300ms. It seemed a much more comfortable delay, and a few of my non-developer friends agreed.

Is there a sweet spot, or am I crazy? Let's just ignore amazon and google's data for the sake of argument.