In a large skillet, cook bacon until crisp. With a slotted spoon, transfer bacon pieces to paper towels to drain; set aside. Reserve drippings.
Stir vinegar and sugar into bacon drippings in skillet. Bring to boiling. Remove from heat and keep warm.
In a salad bowl, gently mix together the lettuce, potatoes, eggs, and onion. Pour warm dressing over. Toss. Sprinkle with bacon; toss again. Makes 6 side-dish servings.