[pcwalton]

Counterpoint: I live in a newly-built condo building near Mission Bay and I don't know of any vacant units in the building. My neighbors very much exist.

These debates always turn into anecdotes that cover up the real reasons why people oppose or support housing—a preference for the suburban or urban lifestyle respectively. People who argue that newly-built condo buildings are mostly vacant always happen to prefer the suburban lifestyle; people who argue that newly-built condo buildings provide much-needed housing always happen to prefer the urban lifestyle (including me). It's all a facade.

The actual vacancy rate in San Francisco, as we expect, is relatively low for US cities.