Sigma customer service is excellent!
Got a lemon 15-30 EX from B&H two months ago and since I couldn't take the lens back to exchange it I had to go to Sigma. I drove 1 and a half hours from NJ to Long Island (Ronkonkoma) and when I got there the technician ask what the problem was and where I live, the guy couldn't believe I drove all way down from NJ. After he checked the lens he gave me a new one. That's an excellent customer service and I believe very few companies treat their customers like Sigma does. Now I've got a 15-30 tack sharp from corner to corner. Thanks Sigma.