Originally Posted by animehawk
Along these same lines, is it possible to use a different thumb image per category?
Yes, each category can be assigned a totally unique image. There are two ways of assigning an image to a category, either through the Gallery CP and then editing the category's properties or when viewing an image if you choose Image Tools there is an option to make the thumbnail for the image that you're currently viewing to the be category's image.
Example of using different images per category: http://www.coolscifi.com/gallery