If using bamboo skewers, soak skewers in water at least 30 minutes. Prepare outdoor grill for direct grilling on medium-high.In blender, puree cilantro, sour cream, mayonnaise, 2 tablespoons lemon juice, vinegar, 1/4 teaspoon salt, and 1/2 teaspoon freshly ground black pepper; set dressing aside.In large bowl, combine shrimp, oil, coriander, remaining 2 tablespoons lemon juice, 1/8 teaspoon salt, and 1/4 teaspoon freshly ground black pepper, tossing until well coated.Thread shrimp, 1/2 inch apart, on skewers. Grill 3 to 4 minutes or until shrimp just turn opaque, turning over once.