I'm working with ArcGis 10 and I need to show the name of the streets along the street line. I want to increase the distance of the label from the line and I saw in the Label Tab I can control this by changing the offset in Placement Properties, but I fear this option does not work when the feature is in a GCS. Is that right?
No, In fact arc map uses map units or page units for label offsets so this distance is not related to projection anyway. As ESRI says "These units are measured in map units or in page units (millimeters, inches, or points)."