A monk's focus allows him to reduce gravity's effects. This feat can be turned off should he desire normal gravity. The Monk must be centered to use this ability, and its ability to reduce falling damage increases every two levels. In practice, even when this feat is turned off, a monk falls more slowly than he would normally.
This class feat does indeed provide a reduced gravity effect as the name suggests, but for the physics-minded of you it does so exactly as it should, scientifically speaking. It does not affect the maximum speed you can reach in a fall due to the effect of gravity, it merely affects the rate at which gravity will increase the speed of your fall, and thus your damage on landing, until Perfect Slow Fall at Monk Level 20. What this means in applicable terms is this: at lower levels of Slow Fall, it will reduce the damage you suffer when falling only on small to medium falls. On longer falls and at higher levels, even with the reduced rate of acceleration, you still have time to reach the maximum fall speed for that distance and will take identical damage whether you use the feat or not. Unlike , monks do not glide as far with Slow Fall in effect, making a feather falling item still useful. (Update 8: A known-bug in the game may cause Slow Fall to be operating, even when the feat is turned off.)