The attached pic shows something that I like to do on my maps: embed photos.
I use real photographs of landscapes, architecture, etc. when designing various worlds and environs. I find it helps to inspire me when I have interesting visuals accessible in my maps. Some interfaces that do this are Google Earth (has little blue clickable square icons which pull up pictures in Panoramio) and Panoramio (has clickkable thumbnails which are nice to look at but obscure the terrain beneath).
This technique is not feasible with bitmap graphic formats, but only with "zoomable" interfaces like SVG, Prezi, or Google Earth. When you click on an area of the map, you zoom in and can see images for that area.
I have used Inkscape to successfully make a map with embedded images. I used Ortelius to make the graphic example below, but it does not export to standard SVG format.
Anyway, I'm hoping that some of you can help me think through what software and/or approaches would work best for this. The real trick is to have the vector portions of the map defined at a large scale that lets you see the whole map, and then have the bitmap portions defined at a very small scale so that they don't interfere with the map but remain high-resolution when you zoom into them.
I hope this line of thinking also encourages others to contemplate a possibly new/interesting element for our maps. :-)