public int CompareTo(object obj)
        {
            if(obj == null)
            {
                throw new ArgumentNullException("Cannot compare to null object");
            }

            PokerCard objAsCard = obj as PokerCard;
            if(objAsCard == null)
            {
                throw new ArgumentException("Cannot compare " + this.GetType().ToString() + " to " + obj.GetType().ToString());
            }

            if(this < objAsCard)
            {
                // preceeds

This is correct:

double e = 2.718281828459045;
int ee = (int)e;
This is not:

double e = 2.718281828459045;
object o = e; // box
int ee = (int)o; // runtime exception
Instead you must do this:

double e = 2.718281828459045;
object o = e; // box
int ee = (int)(double)o;

One last subtlety:

[struct|class] Point {
    public int x, y;

    public Point(int x, int y) {
        this.x = x;
        this.y = y;
    }
}

Point p = new Point(1, 1);
object o = p;
p.x = 2;
Console.WriteLine(((Point)o).x);
What is the output? It depends! If Point is a struct then the output is 1 but if Point is a class then the output is 2! A boxing conversion makes a copy of the value being boxed explaining the difference in behavior.