Rotate an object using the mouse in Unity3D

//How quickly to rotate the object.
var sensitivityX:float = 15;
var sensitivityY:float = 15;

//Camera that acts as a point of view to rotate the object relative to.
var referenceCamera:Transform;

//The script in Start() is executed before Update(), so we can use it to
//doublecheck our variables have valid values before we try to run the script in Update().
function Start() {

    //Ensure the referenceCamera variable has a valid value before letting this script run.
    //If the user didn't set a camera manually, try to automatically assign the scene's Main Camera.
    if (!referenceCamera) {
        if (!Camera.main) {
            Debug.LogError("No Camera with 'Main Camera' as its tag was found. Please either assign a Camera to this script, or change a Camera's tag to 'Main Camera'.");
            Destroy(this);
            return;
        }
        referenceCamera = Camera.main.transform;
    }
}

//Update() is called once every frame, and should be used to run script that
//should be doing something constantly. In this case, we potentially want to
//rotate the object constantly if the user is always moving the mouse.
function Update () {

    //Get how far the mouse has moved by using the Input.GetAxis().
    var rotationX:float = Input.GetAxis("Mouse X") * sensitivityX;
    var rotationY:float = Input.GetAxis("Mouse Y") * sensitivityY;

    //Rotate the object around the camera's "up" axis, and the camera's "right" axis.
    transform.RotateAroundLocal( referenceCamera.up     , -Mathf.Deg2Rad * rotationX );
    transform.RotateAroundLocal( referenceCamera.right  ,  Mathf.Deg2Rad * rotationY );

}