This is why you don't use DateTime

gistfile1.cs

[TestMethod]
public void Subtract_WhenUsingDifferentTimeZones_AreEqual()
{
    // working from my local timezone of +10
    var myTime = new DateTime(2011, 10, 10, 18, 0, 0, 0, DateTimeKind.Local);
    var utcTime = new DateTime(2011, 10, 10, 8, 0, 0, 0, DateTimeKind.Utc);

    var difference = myTime - utcTime;

    Assert.AreEqual(TimeSpan.Zero, difference); // we get 10 hours here
}

[TestMethod]
public void Subtract_WhenUsingDateTimeOffset_AreEqual()
{
    var myTime = new DateTimeOffset(2011, 10, 10, 18, 0, 0, 0, TimeSpan.FromHours(10));
    var utcTime = new DateTimeOffset(2011, 10, 10, 8, 0, 0, 0, TimeSpan.Zero);

    var difference = myTime - utcTime;

    Assert.AreEqual(TimeSpan.Zero, difference); // we get zero here
}