Here is a story about Page Previews:
I was using Wikipedia to research a wildlife refuge in Texas. A picture popped up and I ignored it, moving my mouse to some other area of the screen. But I saw the picture and it left an impression on me. It showed a path leading through a lush green area into a forest. In any case, I finished reading the article and put the wildlife refuge on the short list of places to visit during an upcoming trip.
Later, when planning the trip, I did some deeper research. In doing so, I learned that I had the completely wrong idea about the wildlife refuge. It isn't a lush and forested place; in fact, it has no fresh water and no trees. I went back to Wikipedia to figure out how I had formed such a misguided impression. There, I discovered that the image I associated with the place is really a picture of someplace else. It is an image that pops up automatically whenever a Wikipedia page links to the article on nature trails and the mouse moves over that link.
I now know that this feature which causes potentially unrelated images to pop-up is called "Page Previews" and is intentional.
I know that the people who administer Wikipedia are extremely smart and conscientious, so I'm fairly certain that when they planned this feature, they considered the possibility that attention-grabbing pop-ups might actually detract from their mission, making it more difficult for readers to concentrate on the article at hand, or (as in my case) misinforming readers by presenting images which, in the context of the article, lead to misguided impressions. I'm fairly certain they considered this possibility, but perhaps they regarded it as only theoretical, and they are waiting for feedback from Wikipedia users before they attempt to judge its real impact.
Thus, I wish to state that in my experience the Page Previews feature makes it more difficult to read and understand Wikipedia articles. Please take this into account when planning the future of this feature.
-TC
PS: This page is very hard to find.