Soak about 12 8 to 12-inch wooden skewers in water to cover for at least 30 minutes.
In a large bowl or plastic container, mix together the olive oil, balsamic vinegar, Dijon mustard, garlic, brown sugar, and salt and pepper until well blended. Add scallops and gently toss in the mixture to coat. Let sit at room temperature for 15 minutes, or refrigerate for 1 to 2 hours.
Preheat the broiler or grill. Heat a large skillet over medium heat. Place the pancetta slices in the pan and cook for about 3 minutes on each side until almost cooked through, but still very pliable and not crisp. Remove to a plate lined with paper towels and let cool. Cut into 1-inch pieces.
Skewer the scallops, and pancetta pieces, using two skewers (using two skewers keeps the scallops skewered more securely), and dividing them evenly between the skewers. Discard any remaining marinade. Broil or grill for about 3 minutes on each side, until they are just cooked throughout.
Notes
Scallops are a great fancy meal because small portions suffice since they are so rich.