I remember writing about this for the BBC (to some British backlash) way back in January 2007, when Harj and I decided to leave London for the Valley.

http://news.bbc.co.uk/2/hi/business/6355289.stm

Funny - I mention a chance encounter helping us a lot (meeting FB's head of data at a party), and then the vibe being optimistic and ambitious (and we were working out of the then Twitter office in South Park). We did also bump into Ron Conway one morning on the way back from kickboxing.