Flow maps store directional information in every pixel. They're often used in games to fake flowing fluids, hence the name, but they can also be used to control the direction of anisotropic reflections on a surface. In SR they're used to make specular highlights follow individual hairstrands. Check out this tutorial to see how you can paint them yourself:
http://polycount.com/discussion/98983/how-to-paint-flow-anisotropic-comb-maps-in-photoshop
As for DOB maps, I haven't really figured them out yet. When I once asked Rob Rypka about them, he told me DOB probably stands for "Diffuse Opacity Blend", but also said that no one he asked at the studio knew exactly what they're for. So, I guess a DOB map just contains three otherwise unrelated grayscale textures in its red, green and blue channel.