This question has gotten quite a few votes, but no actual responses to my suggested events.
By my calculations, our 10,000th non-closed question will happen early the day after tomorrow (it being Wednesday here in Australia), on Friday 13th - We are currently at 9946 and running at around 30 questions / day.
So I am going to propose a Friday 13th hectohectoparty consisting of
- A combination answering-and-chat party in the main room
- Encouragement of fun questions on the themes of 10,000, spookiness (it being Friday 13th) and/or celebration.
Assuming this proposal gets enough support, I'll look into how to set up a chat event.
EDIT:
Coming up on the Community Bulletin, starting midnight UTC Friday 13th, chat event and answering party in the main Mathematica.SE chat room!