This is a pretty interesting resource: based on recent census information, the Planning Department has issued a 93-page guide to SF demographics, broken down by neighborhood:

San Francisco at a Glance

Demographics
Total Population 805,240
Group Quarter Population 17,117
Percent Female 49%

Households 324,180
Family Households 44%
Households with Children, Pct of Total 18%
Non-Family Households 56%
Single Person Households, Pct of Total 41%
Average Household Size 2.4
Average Family Household Size 3.5

Click here to see more.