ease_ref.cs

		/// <summary>
		/// Ease vector value
		/// </summary>
		/// <param name="t">Current time (in frames or seconds).</param>
		/// <param name="b">Starting value.</param>
		/// <param name="c">Change needed in value.</param>
		/// <param name="d">Expected easing duration (in frames or seconds).</param>
		/// <param name="easeType">EaseType</param>
		/// <param name="pingPong">use pingpong (optional)</param>
		/// <returns>The correct value.</returns>
		public static Vector2 ChangeVector2(float t, Vector2 b, Vector2 c, float d, EaseType easeType, bool pingPong = false)
		{			
			if (pingPong)
			{
				return new Vector2()
				{
					x = ChangeFloatPingPong(t, b.x, c.x, d, easeType),
					y = ChangeFloatPingPong(t, b.y, c.y, d, easeType)
				};
			}
			else
			{
				return new Vector2()
				{
					x = ChangeFloat(t, b.x, c.x, d, easeType),
					y = ChangeFloat(t, b.y, c.y, d, easeType)
				};
			}			
		}

...
		public static IEnumerator<float> _MoveRectAnchoredPosition(RectTransform rectTransform, Vector2 from,
			Vector2 to, float time,
			EaseType easeType)
		{
			Vector2 diff = to - from;
			float currentTime = 0;
			Vector2 value;
			while (currentTime < time)
			{
				currentTime += Time.deltaTime;
				currentTime = Mathf.Min(time, currentTime);
				value = ChangeVector2(currentTime, from, diff, time, easeType);
				rectTransform.anchoredPosition = value;
				yield return Timing.WaitForOneFrame;
			}
		}
    ...
    
    more code here http://wiki.unity3d.com/index.php?title=Tween =)

EaseConfig.cs

using System;

namespace Utils.Ease
{
    [Serializable]
    public class EaseConfig
    {
        public EaseType EaseType;
        public float Time;
    }
}

RectSnap.cs

using System.Collections.Generic;
using MEC;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;
using Utils.Ease;

public class RectSnap : MonoBehaviour, IBeginDragHandler, IEndDragHandler {
	public float MinimumVelocityToAdjustPosition = 10;
	public EaseConfig MoveEase;
	
	private ScrollRect _rect;
	private bool _isDragging = false;
	
	private float _contentPreviousPosition;
	private bool _makeTween = false;
	void Awake()
	{
		_rect = GetComponent<ScrollRect>();
		_contentPreviousPosition = _rect.content.anchoredPosition.x;
	}

	void Update()
	{		
		if (Mathf.Abs(_rect.velocity.x) < MinimumVelocityToAdjustPosition && _makeTween)
		{
			AdjustPosition();	
		}
	}

	void AdjustPosition()
	{
		_makeTween = false;
		Vector2 globalOffset = GetClosestDistanceToAnyChild();		
		
		Vector2 localOffset = _rect.content.InverseTransformVector(globalOffset);
				
		Vector2 tweenFrom = _rect.content.anchoredPosition;
		Vector2 tweenTo = tweenFrom + localOffset;
		_rect.enabled = false;
		Timing.RunCoroutine(_MakeTween(tweenFrom, tweenTo), "AutoMove");
	}

	/// <summary>
	/// Get Distance to the closest child transform of the content
	/// In GLOBAL coordinates
	/// </summary>
	/// <returns></returns>
	private Vector2 GetClosestDistanceToAnyChild()
	{
		Vector2[] itemsGlobalPositions = new Vector2[_rect.content.childCount];
		for (int i = 0; i < _rect.content.childCount; i++)
		{
			RectTransform childRT = _rect.content.GetChild(i).GetComponent<RectTransform>();
			itemsGlobalPositions[i] = childRT.TransformPoint(childRT.rect.center);
		}

		Vector2 viewPortCenterGlobalPosition = _rect.viewport.TransformPoint(_rect.viewport.rect.center); 

		float minDistance = float.MaxValue;
		Vector2 globalOffset = Vector2.zero;
		for (int i = 0; i < itemsGlobalPositions.Length; i++)
		{
			if (_rect.content.GetChild(i).gameObject.activeInHierarchy)
			{
				float distance = Vector2.Distance(itemsGlobalPositions[i], viewPortCenterGlobalPosition);
				if (distance < minDistance)
				{
					globalOffset = viewPortCenterGlobalPosition - itemsGlobalPositions[i] ;
					minDistance = distance;
				}
			}
		}
		return globalOffset;
	}
	
	
	private IEnumerator<float> _MakeTween(Vector2 from , Vector2 to)
	{
		_rect.enabled = false;
		yield return Timing.WaitUntilDone(Ease._MoveRectAnchoredPosition(_rect.content, from, to, MoveEase));
		_rect.enabled = true;
	}
	
	public void OnBeginDrag(PointerEventData eventData)
	{
		if (_rect.enabled == false)
		{
			Timing.KillCoroutines("AutoMove");
			_rect.enabled = true;
		}
		
		_isDragging = true;
	}

	public void OnEndDrag(PointerEventData eventData)
	{
		_isDragging = false;
		_makeTween = true;
	}
}