Traffic is never bad unless you are traveling during school drop off and pick up. Then you can expect traffic to be backed up into Tiburon in the morning and out of Tiburon in the afternoon. Unfortunately there is usually no way around it unless you want to drive the back side of Tiburon!
Depends where you live in Tiburon. If you live west past Trestle Glen, at any hour it is not a problem. East past Tresle Glen (one lane highway) is a problem at school commute hours, particuarly in the morning 8am til 8:30ish can add 10 minutes (Total 20 minutes) to the commute to the freeway, then from the freeway about half an hour to 40 minutes to San Francisco. From downtown Tiburon to the freeway non commute hours is 10 minutes.
Traffic flows smoothly all the time? Some of the folks there are either heavily sedated or smoking something which I can't afford! You got one road going in and the same one going out! But what a view! Usually THE highest median price in the state next to Santa Barbara. It would be there more often but the numbers are not high enough to give it any statistical validity.
With Tiburon Blvd. being the main way into and out of the city and to highway 101, it can get pretty slow, especially on weekends. Traffic has gotten worse over the years, but if you ask any resident, it's more than worth the it for the benefits of living there.