In a new post from Evil Mad Scientist Laboratories, the clever idea of visual diffs for schematics and board layouts is explored:
GitHub now automatically supports visual diffs for image files included in commits. What this means is that if you (as a designer) generate and include an up-to-date PNG version of your schematic and layout in every version and commit there, you will also automatically generate a matching visual-diff history of the project. This is potentially huge -- if the open source hardware community will step up to the plate and take advantage of it.
http://www.evilmadscientist.com/article.php/visdiff
Cheers,
Drew