I would agree with other posters that bicycling is much more convenient than driving in urban areas largely because of parking. In the central neighborhoods of Seattle, parking can be a nightmare, especially if you're delusional enough to think that you can find a place to park for free. But there are also other considerations, in addition to the ones mentioned by gerv. The main one is traffic density itself; driving around town can get very irritating and stressful, not even considering parking, but you can avoid most of that nonsense just by riding. Even if you need to ride on a busy, backed-up street, a bicycle's small size means you can squeeze through and keep going while cars are stuck in gridlock.
I should point out, though, that the convenience of bike parking is partly a function of the fact that not that many people use bicycles. Lately I've noticed that this advantage has decreased markedly. Just this evening, when I went to meet a friend in Ballard, it took me a few minutes to find a place to lock up my bike because of the sheer number of other bikes. It was still way easier than finding a place to park a car, but a year or two ago, I could have picked any number of places to lock up my bike.