Adapter for Unity that uses the mouse for input if the current device (e.g., the editor) doesn't support acceleration. MIT license, so go nuts.

AccelerometerAdapter.cs

using UnityEngine;
using System.Collections;

public class AccelerometerAdapter : MonoBehaviour {
  public const float TILT_SENSITIVITY = 1.5f;

  public Vector3 Input {
    get {
      if (SystemInfo.supportsAccelerometer) {
        return UnityEngine.Input.acceleration * TILT_SENSITIVITY;
      } else {
        var mousePosition = UnityEngine.Input.mousePosition;
        var x = (mousePosition.x - Screen.width / 2) / Screen.width;
        var y = (mousePosition.y - Screen.height / 2) / Screen.height;
        return new Vector3(x, y, 0) * TILT_SENSITIVITY;
      }
    }
  }
}

InputFilter.cs

using UnityEngine;
using System.Collections;

public class InputFilter : MonoBehaviour {
  public float Filter = 5.0f;
  public float Sensitivity = 4.0f;
  public float XClamp = 3f;
  public Vector3 Input;
  private Vector3 accel;
  public AccelerometerAdapter AccelerometerAdapter;

  void Start() {
    accel = AccelerometerAdapter.Input;
  }

  void Update() {
    // filter the jerky acceleration in the variable accel:
    accel = Vector3.Lerp(accel, AccelerometerAdapter.Input, Filter * Time.deltaTime);

    var dir = accel * Sensitivity;
    dir.x = Mathf.Clamp(dir.x, -XClamp, XClamp);

    Input = dir;
  }
}