With very few exceptions, you should never manually enter a dimension value. I see this all the time when I go to edit dimension text, and the text in the editor reads something like FUTURE 20′ EASEMENT, when it should read FUTURE <> EASEMENT.
Remember, the <> holds the place of the actual linear or angular measurement. If you stretch or reposition a dimension with the hard coded numbers, those numbers do not change. Leave the <> alone. If the dimension value is not what you think it should be, then take a look at what you are dimensioning again.
Update: In AutoCAD 2006, while using the default editor, you no longer see the <> characters, but you now see the actual measurement, highlighted.