Four. I was elected to the Sierra Club San Francisco Local Group and to the SF Bicycle Coalition's board of directors, the largest city-based advocacy org in the country. I was also a (non-elected) board director to my local Community Benefit District here in SF for eight years (which also happens to be the largest in the city) as well as a smaller nonprofit.
This is in addition to my professional experience staffing executive committees within organized labor and being involved in public deliberative bodies. I've got a pretty balanced perspective of the different board governance models.