Yeahhh I'm living in SoMa and paying much, much below the median cost for a 1BR, but I'm thinking of moving out to the peninsula after my lease is up even if I continue working in the city. $200/mo for a Caltrain monthly pass and 1 hour commute one way (on which I can do whatever I want because I'm on a train!) is worth it for me to live closer to my friends (many of whom go to Stanford), not be clumped up with thousands of other people, and have a cheaper apartment.
SF is really going to need to figure out its artificial supply scarcity problems soon.