In March 2009 I came out to give a Google Tech Talk. My flights and hotel were paid for by my stipend, but a few weeks before I came out I saw a "Hacker house" being advertised on HN, on some obscure site called "AirBnB". I stayed on a airbed for $15 a night and met founders of some aspiring startups, notably Wattvision, Divvyshot, 280 North and Airbnb.
This was during demo day, and the energy was just incredible. If it weren't for my girlfriend (now wife), I'd probably have dropped out of college right then and tried to join Wattvision.
Instead, I finished college, got into YC, failed at my startup, then moved back to Dublin, got that compiler job, and then moved to SF. By then I couldn't stop thinking about startups, so when I had enough cash saved my wife let me do a startup again. A year ago I met Allen, and we started https://circleci.com together!
[edit: here's the ad that started it all for me: http://news.ycombinator.com/item?id=494067. Interesting comment on that page: "It seems like http://www.couchsurfing.com/ is a bit more mature than airbnb.com"]