This happens in at least one place in our farm, and until our QA co-ordinator points out other places I cant comment on if this is widespread or not.
On one page, there is an image that appears as a broken image, however going to the picture library shows that it is in fact present and the thumbnail is not broken.
Clicking on the image, goes to a display page with a broken image, however I can download it and it appears fine.
Renaming the image and re-uploading it produces the same thing, a broken image.
This is a 2007 to 2010 upgrade.
Anyone have anything like this occur?