When I insert datetime before 1970 or after 1970, I get different display by db.XX.find();
It displays -2147483647 when I save datetime before 1970
and display 2011 14:59:07 when i save datetime after 1970

The worst thing is that, example:

collection.Insert(new Person

{ Birthday = new DateTime(2000, 1, 1, 0, 0, 0, DateTimeKind.Utc) }

);
var count = collection.Find(Query.GTE("Birthday", new DateTime(1960, 1, 1, 0, 0, 0, DateTimeKind.Utc))).Count()
count will return 0.