The Weather Underground forecast for Seattle says "coldest weather since December 1990 expected during the week ahead."
I remember that December in 1990. I'd gone to Florida to visit family and, unbeknownst to me, the friend driving me to the airport had thoughtfully closed the door between my kitchen and basement, so that the heat couldn't down get to the basement.
Oops. The pipes in the basement then froze.
When a second friend, taking care of the cats, arrived to feed the cats the following day, he noticed that the water was running very, very slowly. So he drove to work on the other side of the lake and then called me in Florida to tell me about the water.
I freaked out. Particularly when he assured me that the kitchen door to the basement had been closed.
I then called a third friend, who rushed over, turned up the heat, opened the door to the basement, got into the basement crawl space, and managed to defrost the pipes before they burst. He then wrapped them with a heating device that turned on when the temperature dropped below 35.
I've only been in the current house for six years. It has a lot of new pipes installed seven years ago, and during the kitchen remodel, that have never been tested in cold weather. Yep, I'm worried.
According to The Straight Dope, letting an interior faucet drip will, in all but the most arctic weather, prevent pipes from freezing. Yes, it wastes water. But it is much cheaper than dealing with the damage from burst pipes.