I got into convertibles upon moving to L.A. With the constant sunshine, it seemed the thing to do. I moved back to Seattle in '90 but couldn't put a lid on it. The old adage "Once you go topless, you can't go back" is true, regardless of the weather.
Convertible converts in Seattle spend 360 days a year scraping moss off their soft tops and shop-vaccing water from the floorboards. We wait patiently for those rare opportunities to air out our roadsters and drive like the wind. The ragtop Rule of the Road is that if the skies are sunny, the lid is down. This often requires serious outdoor outfitting, since there can be wind-chill factors of negative 50 in a 55-mph zone. While seat warmers are currently available on many models (Saabs have the best burn for your buck), a driver's hands and face have the most contact with the elements, making driving gloves and scarves crucial cruising gear, along with a good pair of sunglasses, Chap Stick, a tight-fitting hat, and a flask (as with speed, keep it under the limit).
With weather that changes more often than Greta Van Susteren's mug, it's important to have a convertible that can be converted in a hurry. My first ragtop was a 1986 Jeep CJ-7; in addition to about 100 snaps, the removable doors also had to be jammed into place, making changeovers a 30-minute ordeal. Flick-of-a-switch auto tops are fab—until a fuse or motor goes out; then you're sitting in a bathtub while you putter to the mechanic. The key here is to know your back-up systems, which often involve hand-crank overrides, Gore-Tex, and muscle.
The Northwest has some great driving "trails": The Mountain Loop Highway from Granite Falls to Darrington is a beaut, as are Hurricane Ridge out of Port Angeles and, my favorite, Highway 410 over Chinook Pass, with stunning views of Rainier and Tipsoo Lake (try not to run over backpackers on the Pacific Crest Trail). Closer to home, cruise Lake Washington Boulevard, Harbor Avenue along Alki, and Highway 99 (including the Aurora portion, where going topless often leads to topless conversation). Similar rules apply as with pedestrian hiking: Leave no trace behind (with the exception of your exhaust plume), stay on the path at all times, pay attention to trail markers, and pull over for day-trippers moving at a faster clip.
You can rent a convertible at Budget, 682-2277. The 2002 Ford Mustang convertible runs about $55 a day.