IList<Datetime> Submitted = 
 2012-02-12 10:41:15
 2012-02-13 09:56:02
 2012-02-13 09:56:45
 2012-02-13 12:53:43
 2012-02-13 12:53:57
 2012-02-13 12:53:58
 2012-02-13 00:00:00
 2012-02-15 14:23:46

var list=Enumerable.Range(0,DateTime.DaysInMonth(2012,2)).Select(i=>new DateTime(2012,2,1).AddDays(i)).ToList();
IList<DateTime> dList = new List<DateTime>();
dList = list.Except(Submitted).ToList();  //这个地方得出的还是29，没有和Submitted比对成功啊，应该怎么办？？

dList = list.Except(Submitted.Select(p=>p.Date)).ToList();

------解决方案--------------------

C# code
            IList<DateTime> Submitted = new List<DateTime> { Convert.ToDateTime("2012-02-12 10:41:15"), Convert.ToDateTime("2012-02-13 09:56:45"), Convert.ToDateTime("2012-02-13 09:56:02"), Convert.ToDateTime("2012-02-15 14:23:46") };
            var list = Enumerable.Range(0, DateTime.DaysInMonth(2012, 2)).Select(i => new DateTime(2012, 2, 1).AddDays(i)).ToList();
            IList<DateTime> dList = new List<DateTime>();
            list.Except(Submitted,new DateTimeCompare()).ToList().ForEach(x => Console.WriteLine(x.ToString("yyyy-MM-dd")));
        public class DateTimeCompare : IEqualityComparer<DateTime>
        {
            #region IEqualityComparer<DateTime> 成员

            public bool Equals(DateTime x, DateTime y)
            {
                if (x.ToString("yyyy-MM-dd").Equals(y.ToString("yyyy-MM-dd")))
                    return true;
                else
                    return false;
            }

            public int GetHashCode(DateTime obj)
            {
                return obj.Year + obj.Month + obj.Day;
            }

            #endregion
        }