Unity3d lifting platform (no lag) dont use it!!! see https://gist.github.com/nicloay/9662874

LiftingPlatformController.cs

using UnityEngine;
using System.Collections;

public class LiftingPlatformController : MonoBehaviour {

	public float routeLenght = 10;
	public float verticalSpeed = 10;
	[Range (0,1)]
	public float startRelativePosition=0;

	public bool goUp;
	Vector3 basePosition, remotePosition;
	void Start(){
		basePosition = transform.position;
		remotePosition = getRemotePosition();
		transform.position = Vector3.Lerp(basePosition, remotePosition, startRelativePosition);
		updateVelocity();
	}

	Vector2 velocity;
	void Update(){
		if (goUp && (transform.position.y - remotePosition.y) > 0){
			goUp = false;
			updateVelocity();
		} else if (!goUp && (transform.position.y - basePosition.y) <0){
			goUp = true;
			updateVelocity();
		}
		rigidbody2D.velocity = velocity;
	}

	void updateVelocity(){
		velocity = new Vector2(0, goUp ?  verticalSpeed : -verticalSpeed);
	}

	Vector3 getRemotePosition(){
		return basePosition + new Vector3(0, routeLenght, 0);
	}
	

	void OnDrawGizmos(){
		if (Application.isPlaying){
			Gizmos.DrawLine(basePosition, remotePosition);
		} else {			
			Vector2 boxSize = (collider2D as BoxCollider2D).size; 
			basePosition = transform.position;
			remotePosition = getRemotePosition();
			Gizmos.DrawLine(transform.position, remotePosition);
			Gizmos.DrawCube(Vector3.Lerp(basePosition, remotePosition, startRelativePosition),boxSize);
		}

	}
}