GREY'S ANATOMY - "What a Difference a Day Makes" - George helps his best friend, Izzie, down the aisle for her wedding to Alex, on "Grey's Anatomy," THURSDAY, MAY 7 (9:00-10:02 p.m., ET) on the ABC Television Network. KATHERINE HEIGL, T.R. KNIGHT, SANDRA OH, MICKEY MAXWELL, JUSTIN CHAMBERS, ELLEN POMPEO