I have recently noticed that certain kinds of pictures look really bad as thumbnails, but quite good at larger sizes. Also sometimes to get a picture to look good as a thumbnail it looks unnatural at full sized. I have three versions of a picture up where the one whose thumbnail looks the best, looks horribly oversaturated when seen full sized, and the one that I think looks best full sized look washed out in its thumbnail.
Also it seems in general that simple pictures that have quick, but not lasting appeal catch your eye best in thumbnails, so I am beggining to wonder if this system encourages a dangerous overemphasis on such pictures. Anybody else have any thoughts about this?