Ask HN: What kind of effect will working in SF have on my network?

If I move to San Francisco and work for a startup there, I imagine my network will grow immensely. First, can anyone give first-hand accounts of this? More importantly, I don't want to stay there for more than 3-5 years. Can anyone speak to the effect this will have on my network nationally? Would I be better of moving to a certain city to build my network there or will my SF network reach out significantly to other cities as well? Any facts or experiences are greatly appreciated as this is a strong consideration for an offer I have now.