Late blight is back on the east coast. There have been positive ids on tomato plants in North Carolina, New York and Pennsylvania. Late blight is hard to battle, since it can rapidly spread great distances and its affect on tomatoes and potatoes is distressingly quick. Home gardeners and commercial farmers can see their entire crops wiped out, so it's important to get a definitive id from your local Cooperative Extension Service as soon as you suspect late blight. They have the means to get the word out and warn other growers.
Late blight tends to start out as gray blotches and only yellows as it ages. You may even get a ring of white mold around the spots, if the weather is particularly wet and damp. Here are some great photos of the symptoms of late blight, from the USDA.