Normally, I'm a strong advocate for always drawing objects at full size (1:1) and for never overriding the default dimension text. However, there may be times when one or both of those objectives aren't feasible. Or you just may have a misbehaving dimension, and this post might help you set it straight.
The key (or the culprit, depending on your point of view) is the DIMLFAC system variable, also available on the Primary Units tab of the Dimension Style Manager.
By default, this is set to 1, and in most situations should probably stay that way. If you set DIMLFAC to a smaller number, say 0.5, a dimension for a 1" line will display 1/2". If DIMLFAC is bigger than 1, say 2, a dimension for a 1" line will display 2".
Again, I'm expecting that this will help you more for troubleshooting than for practical applications, but it's here if you need it.