you can use AngryAnt's copy inspector script. the script can copy and paste any component.

There isn't any way currently to copy/paste variable values in the inspector.

Since individuals variables cannot be copied in the inspector (unless they happen to be strings or ints), I wrote a custom editor for GUISkin. To use it, save the following as Assets/Editor/GUISkinExtensions.js. You should then get extra lines at the bottom of the inspector for a GUISkin that allow you to copy styles. I find this very useful when you want to make a variation of an existing styles - if it's a custom style you can just CTRL-D to duplicate, but if it's a builtin like label, you need this script.

// See http://answers.unity3d.com/questions/9844/copypaste-guistyle-in-the-inspector.html
//
@CustomEditor(GUISkin)
class GUISkinExtensions extends Editor
{
    static final var builtinGUISkinStyles : String[] = [
       "box", "button", "toggle",
       "label", "textField", "textArea",
       "window",
       "horizontalSlider", "horizontalSliderThumb",
       "verticalSlider", "verticalSliderThumb",
       "horizontalScrollbar", "horizontalScrollbarThumb",
       "horizontalScrollbarLeftButton", "horizontalScrollbarRightButton",
       "verticalScrollbar", "verticalScrollbarThumb",
       "verticalScrollbarUpButton", "verticalScrollbarDownButton",
       "scrollView"
    ];

    var from = 0;
    var to = 0;

    function OnInspectorGUI()
    {
       var skin = target as GUISkin;

        DrawDefaultInspector();

       EditorGUILayout.Space();

       var names = builtinGUISkinStyles;
       var customNames = new String[skin.customStyles.Length];
       for (var i=0; i<customNames.Length; ++i) {
         customNames[i] = skin.customStyles[i].name;
       }
       names += customNames;

       from = EditorGUILayout.Popup("From:",from,names);
       to = EditorGUILayout.Popup("To:",to,names);
       if (GUILayout.Button("Copy")) {
         var fs = skin.GetStyle(names[from]);
         var ts = skin.GetStyle(names[to]);
         var newStyle = new GUIStyle(fs);
         newStyle.name = ts.name;
         var custom = to - builtinGUISkinStyles.Length;
         if (custom >= 0) {
          skin.customStyles[custom] = newStyle;
         } else {
          skin.GetType().InvokeMember(names[to], System.Reflection.BindingFlags.SetProperty, null, skin, [newStyle]);
         }
       }
    }
}

I encountered a similar need, since our skin had a ton of custom styles. Since GUISkins have the property of saving modifications made to them while playing the game, I made a this quick and dirty script that lets you duplicate, delete and sort your skin's custom styles. It is also helpful when you just want to see what is in a skin.

Nothing fancy, but I've found it very useful.

using UnityEngine;
using System;
using System.Collections;

//
//  Some functionality to clean up skins with lots of custom styles
//  Since skins are saved even while playing, we can just play and edit
//  Usage
//     - new scene
//     - add an empty game object
//     - add this script to that object
//     - set the skin to the one you want to edit
//     - play
//
public class SkinHelper : MonoBehaviour 
{
    public GUISkin skin;

    private Vector2 scrollView;
    private Rect area;
    private string customText = "Button";

    void Awake()
    {
    	area = new Rect(0,0,Screen.width, Screen.height);
    }

    void OnGUI() 
    {
    	if( skin == null )
    	{
    		GUILayout.Label("No skin set for SkinHelper");
    		return;
    	}

    	GUILayout.BeginArea( area );

    	GUILayout.BeginVertical();
    		GUILayout.BeginHorizontal();
    			GUILayout.Label("Skin: " + skin.name);
    			GUILayout.Label("Custom Styles: " + skin.customStyles.Length);
    			if( GUILayout.Button("Sort by name") )
    			{
    				Array.Sort( skin.customStyles, StyleComparer );
    			}
    		GUILayout.EndHorizontal();

    		// column headers
    		GUILayout.BeginHorizontal("Box");
    			GUILayout.Label("Custom Styles", GUILayout.Width(area.width*0.2f));
    			Rect r = GUILayoutUtility.GetRect( new GUIContent("Duplicate"), "Button" );
    			Rect r2 = GUILayoutUtility.GetRect( new GUIContent("Delete"), "Button" );
    			GUI.Label(new Rect(r.x,r.y,r.width+r2.width,r.height), "Operations");

    			GUILayout.Label("Examples");
    			GUILayout.FlexibleSpace();
    			GUILayout.Label("Custom Text:");
    			customText = GUILayout.TextArea( customText );
    		GUILayout.EndHorizontal();


    		scrollView = GUILayout.BeginScrollView( scrollView );
    			GUILayout.BeginVertical();

    			foreach( GUIStyle cust in skin.customStyles )
    			{
    				GUILayout.BeginHorizontal();
    					GUILayout.Label(cust.name, GUILayout.Width(area.width*0.2f));
    					if( GUILayout.Button("Duplicate") )
    					{
    						DuplicateStyle( cust );
    					}
    					if( GUILayout.Button("Delete") )
    					{
    						RemoveStyle( cust );
    					}
    					// some examples
    					GUILayout.Label("Label", cust );
    					GUILayout.FlexibleSpace();
    					GUILayout.Box("Box", cust );
    					GUILayout.FlexibleSpace();
    					GUILayout.Button(customText, cust );
    					GUILayout.FlexibleSpace();
    					GUI.enabled = false;
    						GUILayout.Box("Disabled Box", cust );
    						GUILayout.FlexibleSpace();
    						GUILayout.Button("Disabled Button", cust );
    						GUILayout.FlexibleSpace();
    					GUI.enabled = true;
    				GUILayout.EndHorizontal();
    			}

    			GUILayout.EndVertical();
    		GUILayout.EndScrollView();

    	GUILayout.EndVertical();

    	GUILayout.EndArea();

    }

    int StyleComparer( GUIStyle x, GUIStyle y )
    {
    	return String.Compare( x.name, y.name );
    }

    void RemoveStyle( GUIStyle style )
    {
    	int removeIdx = Array.IndexOf( skin.customStyles, style );
    	if( removeIdx < 0 )
    		return;

    	// move each item back one, then resize off the end
    	for( int i=removeIdx+1; i<skin.customStyles.Length; i++ )
    	{
    		skin.customStyles[i-1] = skin.customStyles[i];
    	}
    	Array.Resize( ref skin.customStyles, skin.customStyles.Length-1 );
    }

    void DuplicateStyle( GUIStyle style )
    {
    	Array.Resize( ref skin.customStyles, skin.customStyles.Length+1 );
    	skin.customStyles[skin.customStyles.Length-1] = new GUIStyle(style);
    	skin.customStyles[skin.customStyles.Length-1].name += " Copy";
    }
}