Hey gang. Pete, I'm looking foward to it. I'm not the best photographer in the world (lots of thumbs and headless folk) but I'll take what pics I can.  Billy, a real fast and dirty explanation is that displacement maps move the vertices of a mesh based on color values (black-grey-white)...kind of like a hieght map in a terrain editor. It allows you to simulate higher res detail on lower res meshes, assuming the low-res mesh has enough polys to support that detail, all based on image data. Most folks use ZBRUSH to paint their maps directly on a subdivided mesh. Usually, the low res mesh used in the final image is taken into ZBrush (or simillar app), subdivided 3 to 7 times and then they use a "brush" to move vertices around to add detail. This gets exported as an image which is applied to the low res model that shares UV info with the highres one. The effect only appears at render time, dramatically lowering the file size of a scene while allowing models to appear to have more detail than normally possible.

I think that explained it more or less...explanations were never my thing. Examples...now that I can do. :)

Here's my ref.