An excellent survey of the PCF technique was written by Fabio Pellacini of Pixar, and can be found in Chapter 11, Shadow Map Anti-aliasing, of GPU Gems, edited by Randima Fernando, Addison-Wesley Professional, 2004. If more details are desired, I highly recommend reading this short, but informative, chapter.
Because of its simplicity and efficiency, the PCF technique is an extremely common method for anti-aliasing the edges of shadows produced by shadow mapping. Since it has the effect of blurring the edges, it can also be used to simulate soft shadows. However, the number of samples must be increased with the size of the blurred edge (the penumbra) to avoid certain artifacts. This can, of course, be a computational roadblock. ...
