Standard toolbar settings are maintained within the default template (Normal.mxt) only.
Custom toolbar settings are maintained within the default template, or the current map document (.mxd). When saved within a map document (.mxd) custom toolbars are maintained solely within that document. The settings are maintained if the document is copied to another machine, or opened by another user, and even when they toolbar itself is turned off, but they will not appear in any other documents.
ArcGIS 9.0 and 9.0 Sp1 maintain custom toolbars only when they are turned on within the document (.mxd).