"I just came back to this thread to ask what double-sides actually did do, because they weren't acting how I wanted them."

double face means that the face will be visible from both side.
By default, in blender or in Poser rendering shows both side of a single face.
But in Blender video game or with Poser in preview mode only one side of the face will be visible.
The one identify by the rotation direction of the point creating the face (FYI).
Be care, if double faces works fine in Poser4, I am not sure it will works fine in next releases.
"Adding second sides to things almost requires instruments that can measure objects on an atomic level."
No, UVmapper have a feature to do it. But I do not remember if this feature is only available in the commercial version or in the free version too.