Guys, the backface masking for brushes is like a dream come true for low-poly painting.
Really, really good stuff. Thanks.
Hey Reactor whats back face masking?
Sorry I came back here after a long time.
I am scared that it will take me another year to learn zbrush 3 and by then z 4 will be out. 
Heh, I know what you mean To find these options just look under your brush menu (at the top). You’ll see options for Cavity, Color and Backface masking. Hold control over each- the descriptions explain things well.
For sharp edged objects the backface masking (best controlled with the curve) prevents paint from slipping off one edge and creating a smeared look down a face you didn’t want it to. Take a cube, for example. Face it straight on, and try painting the front face without the sides being smeared. Then you’ll know why being able to restrict painting to certain faces (depending on angle) is awesome. Some people might suggest masking off faces to prevent painting on certain ones, but that’s a slow and clunky operation when you’re working on a complex low-poly model. This way is much friendlier.
Accept my vanks dear Reactor for attracting me to the backface Masking button.
I was dreaming just about such functon to desactivate the nearest surface of the mesh but could not understand it.
You cannot imagine my delight now.
Thank you and Pixologic a whale !
Anatom
No worries… good to know someone else is going to enjoy using it 
Backface masking is fantastic. Try inverting the default curve and using it with RGB, RGB+Texture+Alpha. Who needs lights! 