We accepted Bitcoin for the 5th Future of Money & Technology Summit which took place on December 9th of last year. The Future of Money & Technology Summit covered some Bitcoin related topics, but is much more around general payment innovations then strictly about Bitcoin. I'm interested if anyone actually sold tickets for Bitcoin before that.
We also sell tickets for the SF MusicTech Summit for Bitcoin. Wasn't sure if we were the first, but others have mentioned they think we were. Do want to place the stake in the ground in case folks who started accepting Bitcoin for tickets after our events wish to claim that they were the first, even though we preceded them. That said, the more, the merrier.
All the best, and thanks!