Sunday is just a stroll in the park for the riders. It's the day they have the 1-2-3 photo shots of the riders holding glasses of champagne and riding along holding hands. The motorcycle crews have their day of fun as well doing silly shots with the cameras. The distance is not long enough to make it competitively useful, though there have been exceptions in the past. The last stage is the pinnacle for the sprinters as no stage win rivals the Champs Elysees (sp?) in Paris.
I think the rules of the last stage give all riders the same time if they finish within 1km of the first rider to cross the line? As it's a flat stage, don't expect anything dramatic apart from the flat-out boys.
The tour will be won by Armstrong or by Ulrich on the Saturday TT. Sunday will not make a difference.