Windows 7 Professional - Nvidia GeForce GTX 760
In 3D window Properties panel the Dimensions XYZ stepping arrows add or subtract 0.01 Blender units per press.
If however the Units of the scene are changed from 'None' (default Blender units) to either 'Metric' or 'Imperial' then the stepping arrows now add or subtract in whole units. This increment is far greater than is useful and is unexpected behaviour for the user.
For example, if the scene is set to metric units each press of the arrow in Dimensions will add or subtract an entire meter rather than the expected one-hundreth of a meter.