1. Weigh down cedar planks with a heavier object in a large container. Add water to cover, and soak at least 8 hours.
2. Combine dill and next 5 ingredients; set aside.
3. Sprinkle salt and pepper evenly on salmon.
4. Remove cedar planks from water, and place planks on cooking grate on grill.
5. Grill soaked planks, covered with grill lid, over medium-high heat (350° to 400°) 2 minutes or until the planks begin to lightly smoke. Place 2 fillets on each cedar plank, and grill, covered with grill lid, 15 to 18 minutes or until fish flakes with a fork. Remove fish from planks to individual serving plates using a spatula. (Carefully remove planks from grill using tongs.) Spoon herb mixture over fish, and serve immediately.