gistfile1.cs

        [Test]
        public void ShouldNotCopyTheId()
        {
            Mapper.Reset();
            Mapper.CreateMap<Mark, Mark>();
            Mapper.CreateMap<Foo, Foo>().ForMember(foo => foo.Id, opts => opts.Ignore());

            var mark = new Mark { Foos = new List<Foo> { new Foo { Id = Guid.NewGuid()}}};
            var newMark = Mapper.Map<Mark, Mark>(mark);

            Assert.That(newMark.Foos[0].Id, Is.EqualTo(Guid.Empty));
        }

    public class Mark
    {
        public List<Foo> Foos { get; set; }
    }

    public class Foo    
    {
        public Guid Id { get; set; }
    }

NUnit.Framework.AssertionException:   Expected: 00000000-0000-0000-0000-000000000000
  But was:  b94fb309-5af8-4740-984f-602cf6308c89