Ok...transform.Translate invalidates the rigidbody.AddForce. Merging these two scripts wouldn't help. Either use AddForce for the tilting or split the scripts even more: Parent the ball to an empty, attach the bounce script to the ball and the tilt script to the empty.

opps, scripts would help!

This is the tilt script

// Move object using accelerometer
var speed = 10.0;

function Update () {
    var dir : Vector3 = Vector3.zero;

    // we assume that device is held parallel to the ground
    // and Home button is in the right hand

    // remap device acceleration axis to game coordinates:
    //  1) XY plane of the device is mapped onto XZ plane
    //  2) rotated 90 degrees around Y axis
    dir.x = -Input.acceleration.y;
    dir.z = Input.acceleration.x;

    // clamp acceleration vector to unit sphere
    if (dir.sqrMagnitude > 1)
        dir.Normalize();

    // Make it move 10 meters per second instead of 10 meters per frame...
    dir *= Time.deltaTime;

    // Move object
    transform.Translate (dir * speed);


}

and the bounce script

var speed : float = 0.1;
function Update () {
    for (var i = 0; i < Input.touchCount; ++i) {
        if (Input.GetTouch(i).phase == TouchPhase.Began) {
        print ("touched");
        gameObject.rigidbody.AddForce(new Vector3(20, 360, 50), ForceMode.Force);
        }
    }
}

Thanks

Yes put it in one script.

If you have two independend Update functions, you can never know which on is called first. So the two position changes may or may not combine as you wish, and that each frame. There are ways to provide that via Script Execution Order Settings, but I would handle the movement of one object in one Script. Otherwise you would have a lot more work to have it consistently and the possibility of hard to find errors is reduced.

For more info we gotta take a look at your scripts.