Cut potatoes into 1/2 inch pieces; place in a medium sauce pan; cover with cold water. Bring to a boil, reduce heat and simmer 10 - 15 minutes or until tender. Do not overcook. Drain and cool. In a large bowl combine the potato, onion, celery and pimento; toss gently. In a small bowl, mix together the mayonnaise, yogurt, sour cream, mustard and vinegar; add to potato mixture; toss gently to coat. Add salt and freshly ground pepper, to taste. Refrigerate for at least an hour to allow the flavors to develop.
Per Serving: 199 Calories (27.8% from fat); 6g Fat (1g Sat, 1g Mono, 1g Poly); 5g Protein; 32g Carbohydrate; 3g Dietary Fiber; 9mg Cholesterol; 368mg Sodium. Food Exchanges: 1 1/2 Grain (Starch); 1 Fat.