Here is what the wiki says on the subject:
Face Painting: By default, you will be painting the whole mesh and it will look solid. RMB clicking will pick up the color from the mesh at that point. To only paint part of the mesh, press F in 3D View to highlight the UV/Face edges. The faces of the mesh will be outlined for you using the red-green edges in the 3D View, and if you have Shadow Mesh enabled in the UV/Image Editor, the UV Layout will also be shown as a gray outline in the UV/Image Editor window. Now, RMB will select a face, and Shift RMB will select multiple faces. To only paint part of the mesh, press H to Hide the selected Faces when in Texture Paint mode. Just like when editing a mesh, doing a Border select with the LMB button selects only certain faces. Doing a Border select with the RMB button excludes those faces from the selected set of faces.
Selecting some faces and pressing H Hides them from view and thus painting. It also continues to hide them during textured viewport shading in Object view. During your painting session with F active, or in UV Face Select Mode, Alt H un-hides them. Unfortunately, H and Alt H don’t do anything when you are not in this face-select sub-mode (because there aren’t faces ‘selected’).
After some testing what I find is that if you start painting on a visible face and continue that same stroke past the visible edge to where a hidden face is, the hidden face does receive the color. However, if you start a new stroke where a hidden face is you get no color. So the wiki is about half right I guess.