Hi Ori,
As some people do not care a lot for beta features or new features, do
not read the mailing lists and overlook main discussion forums or are just unable to understand English, they were surprised and confused and wondered how they could disable the feature.
Surprised and confused is a good description of how I feel when I visit the main page of Commons and my mouse cursor strays onto the picture of the day. A purple hazard light flares along the edges of the image, presumably intending to alert me to the gross misuse of JavaScript that is about to occur. Then the image pops out like some demented, angry Jack-in-the-box, only nominally larger then the original image (which is still visible below it), but transposed so that it obscures interface elements and page text.
Unless I am mistaken, this is galleryZoomHover.js [1]
It has never been made into a gadget.
You and I are two of the mere 11 users (is Special:Search is to be trusted) to have activated this piece of JavaScript in their common.js :-)
[1] <https://commons.wikimedia.org/wiki/User_talk:Rillke/galleryZoomHover.js