Cook potatoes in boiling salted water 20 minutes or until potatoes are tender. Drain well, and cool. Peel potatoes, and cut into 1/2-inch cubes.
Slice eggs in half lengthwise, and carefully remove yolks. Mash yolks in a medium mixing bowl. Add vinegar, mustard, horseradish, mayonnaise, sour cream, salt, and celery salt; mix well. Chop whites, and add to yolk mixture. Add potatoes, celery, onion, green pepper, and pimiento, stirring until well blended. Cover and refrigerate at least 1 hour. Garnish with cucumber slices, if desired.