Preheat oven to 425 degrees. Bake potatoes 50-60 minutes. Or you may bake them in microwave.
Meanwhile, combine sour cream and mayonnaise in bowl. Chop bacon, red onion and celery; add to sour cream mixture. Stir in salt and pepper; cover. Refrigerate until ready to serve.
Remove potatoes; cool completely. Coarsely chop potatoes into 1/2 inch pieces. Place in large bowl; fold in sour cream mixture. Cover and refrigerate 4-6 hours or overnight. Garnish with sliced green onion and cheddar cheese, if desired.