Exploring some C# in Unity. Reading through and implementing one of the recipes found in Unity 4.x Cookbook, http://www.packtpub.com/unity-4-x-cookbook/book.

CursorScript.cs

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using System.Linq;

public class CursorScript : MonoBehaviour {

  public Texture2D iconArrow;
  public Vector2 arrowRegPoint;
  public Texture2D iconZoom;
  public Vector2 zoomRegPoint;
  public Texture2D iconTarget;
  public Vector2 targetRegPoint;

  private Vector2 mouseReg;

  private delegate bool WhenActionPerformed();
  private delegate void ExecuteThisAction();

  private Dictionary<WhenActionPerformed,ExecuteThisAction> actions;

  void Start () {
    setCursorToArrow();
    guiTexture.enabled = true;
    actions = new Dictionary<WhenActionPerformed,ExecuteThisAction>();

    addAction(
      whenThisIsTrue: () => { return Input.GetKey(KeyCode.RightShift) || Input.GetKey(KeyCode.LeftShift); },
      performAction: () => setCursorToTarget()
    );

    addAction(
      whenThisIsTrue: () => { return Input.GetMouseButton(1); },
      performAction: () => setCursorToZoom()
    );

    // This is the fallback action which will always be true
    addAction(
      whenThisIsTrue: () => { return true; },
      performAction: () => setCursorToArrow()
    );
  }

  void Update () {
    Vector2 mouseCoord = Input.mousePosition;
    Texture mouseTex = guiTexture.texture;
    guiTexture.pixelInset = new Rect(mouseCoord.x - mouseReg.x,
      mouseCoord.y - mouseReg.y,
      mouseTex.width,
      mouseTex.height);

    takeAppropriateAction();
  }

  private void addAction(WhenActionPerformed whenThisIsTrue,ExecuteThisAction performAction) {
    actions.Add(whenThisIsTrue,performAction);
  }

  private void takeAppropriateAction() {
    actions.First(keyPair => keyPair.Key()).Value();
  }

  private void setCursorToTarget() {
    setCursorToTextureAtPoint(iconTarget,targetRegPoint);
  }

  private void setCursorToZoom() {
    setCursorToTextureAtPoint(iconZoom,zoomRegPoint);
  }

  private void setCursorToArrow() {
    setCursorToTextureAtPoint(iconArrow,arrowRegPoint);
  }

  private void setCursorToTextureAtPoint(Texture texture,Vector2 regPoint) {
    if (texture) {
      guiTexture.texture = texture;
      mouseReg = regPoint;
      Screen.showCursor = false;
    }
  }

}