The shoe probably cost Tanui the gold, but not in the way you think. First off, Haile only ran into him because Tanui was playing tactical games and slowing down (They ran 69 for the penultimate lap). When his shoe comes loose he wastes a ton of energy flailing his arms up in the air and then (probably from the surge of adrenaline) starts sprinting like a mad man with a full lap to go and then faids down the home stretch.
Yes I remember watching that live and that's one Gold Medal that Geb may not have won if not for that incident!
In hindsight, he probably would have had a better chance if he'd calmly moved into lane 2, let Haile go by on his indide while he's kicking the shoe off, sat behind Haile for 300 meters and then tried to sprint around him off the final turn. To bad you can't think that logically when your shoe comes off while running a 55 second last lap with a gold medal on the line.