It was when we went to a meet up Facebook Developers (as in, developers around the world who make applications etc.) and Matt (a Facebook Developer as in, he works for Facebook!) gave a talk on the new Graph API.
The new basis for the Facebook API sounds like a wish come true for Developers - as the originally was notoriously buggy, and this new version sounds simple to use and smooth to run.
We met Matt just after building the "More Friends Than Tigers" Facebook App for the BBC, as part of their publicity for the fundraising night "Wild Night In" on BBC 2 on the 20th June. With £1,000,000 raised, it was a roaring success (sorry!).