// Scale a button by 1.5 times each time is pressed.

private var scale : Vector2 = Vector2(1,1);
private var pivotPoint : Vector2;

function OnGUI () {   
    pivotPoint = Vector2(Screen.width/2,Screen.height/2);
    GUIUtility.ScaleAroundPivot (scale, pivotPoint); 
    if(GUI.Button(Rect(Screen.width/2-25, Screen.height/2-25, 50, 50),"Big!")){
        scale += Vector2(0.5,0.5);
    }        
} 

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    private Vector2 scale = new Vector2(1, 1);
    private Vector2 pivotPoint;
    void OnGUI() {
        pivotPoint = new Vector2(Screen.width / 2, Screen.height / 2);
        GUIUtility.ScaleAroundPivot(scale, pivotPoint);
        if (GUI.Button(new Rect(Screen.width / 2 - 25, Screen.height / 2 - 25, 50, 50), "Big!"))
            scale += new Vector2(0.5F, 0.5F);
        
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    private scale as Vector2 = Vector2(1, 1)

    private pivotPoint as Vector2

    def OnGUI():
        pivotPoint = Vector2((Screen.width / 2), (Screen.height / 2))
        GUIUtility.ScaleAroundPivot(scale, pivotPoint)
        if GUI.Button(Rect(((Screen.width / 2) - 25), ((Screen.height / 2) - 25), 50, 50), 'Big!'):
            scale += Vector2(0.5F, 0.5F)