SFPUG meeting at which Mike Kreiger of Instagram explained how they grew and eventually sharded their 2TB of Postgres data to support 27 million users. It's a great presentation which explains the growth process of a successful web/mobile startup, as well as horizontally scaling PostgreSQL.
Yes, you too can use PostgreSQL to make One Billion Dollars!
Video is on UStream. Sorry you can't see the slides on the video; we had technical issues with the camera. Slides are here, you can click along with Mike talking on your own.