That question depends on, first of all, what time of the day will you be commuting into SF?
If you are going in during "normal" business commute times, I won't kid you the traffic definitely backs up, mainly before the San Anselmo hub, after that you can either head down Redhill Blvd (towards San Rafael off 101) which is actually a quicker commute as opposed to on Sir Francis Drake (Greenbrae exit of 101). THe distance is closer to the 101 (meaning less surface roads) even though you are 2 exits north on 101. The traffic lights are timed and the street is one-way, which really speeds things up.
If you are commuting during off hours, the drive isn't bad, I would say you could get into and out of SF in about 25-30 minutes. During commute times, I'd say 45 - 60 minutes. That's into SF. That doesn't account for the time it might take you within SF to get to your destination.
I would estimate commute times to be: am: 7:00 - 8:30, and evenings, 4:30 - 6:30.
If you were to look in San Anselmo, especially homes that are located before the "Hub" intersection, you could cut 15 minutes off your commute time if it's during commute hours.
Fairfax is a wonderful community, I'd recommend talking to folks who live there and commute and ask them directly! I'm happy to get you in touch with folks if you like, just let me know. (As I live in San Rafael)
Hope that helps!