I can't find the post but since the generation of blocks rather than the calendar time is more important, there have been suggestions to not use calendar time then to mark a "birthday".

Since bitcoin has an event every 210,000 blocks whose timing roughly correlates to an occurance once every four years, how about timing the event to one fourth of that 210,000 blocks.  Or every 52,500 blocks -- roughly one year, but will vary based on rates of change of difficulty.  This would put the birthday in December this year.  About December 9th, to be more specific.

How about April 17th so that we can both rejoice and be reminded that the game is not over yet?

    did anything happen last week?

yeah, block height is cooler.

but 262,500  hmmmm   315,000, 367,500,...   why did the great one not make it every 200,000 blocks 

edit: also the block reward change is a big event of its own - we need an additional bitcoin day

to be honest I had hoped for a date that would come up in the next couple of months...

@Phin: you are classic


another date of importance is the creation date of satoshi's paper: March, 24th 2009

that is the thing!

bitcoin pizza day! on that day every bitcoin believer must order a pizza for bitcoins!

Looking forward to the day I get 10.000 pizzas for two bitcoins 

Why does it have to be every year? Why can't it be every four years like the Olympics or the World Cup. It will make it a more special celebration people will look forward to.
I like it having a floating date instead of pinning it down, and will make it something that will generate a lot of buzz and anticipation as the date approaches. That may make it like the flash mob phenomena in some ways.

/edit the best celebrations are not those we plan and organize ahead of time but those which just happen... organically; spontaneously.    

The block-parties every 210,000 blocks will surely happen anyway, so we already have such a very special celebration.

It can't hurt though to have another Bitcoin day to celebrate every year and a floating date according to block-height would be very appropriate. I like the 52,500th block idea since it is the most logical one, but it will probably stay in winter for a long time. Anyway, here's a few alternatives from the top of my head:

- Once every 50,000 blocks or roughly 11.6 months. Pretty intuitive, would not collide with the block-partys and soon be in summer. Projected dates for the next 5 years:

• 2012: October 1st
• 2013: September 13th
• 2014: August 26th
• 2015: August 8th
• 2016: July 21st

- Once every 2^16=65536 blocks or roughly every 15 months. Would not collide with a block-party within the next 50,000 years but there would be years without a Bitcoin day and it is probably a bit too nerdy - even for Bitcoin Projected dates for the next 5 years:

• 2012: September 7th
• 2013: December 6th
• 2014: none
• 2015: March 6th
• 2016: June 4th

- Pick a good (notable) calendar date and take the nearest 10,000th block. That would mean it could only vary about +-2 months around that day and therefore stay roughly in the same season every year.

- Celebrate the 10th difficulty adjustment every year. Would always be around spring.

- Countdown to the last Satoshi. The block with the last Satoshi ever to be mined will be 6,929,999. Divide that by 100 and you have kind of a percentage counter for Bitcoin which will increase roughly every 16 months. A nice property but maybe too long a cycle. Projected dates for the next 5 years:

• 2012: November 25th
• 2013: none
• 2014: March 21st
• 2015: July 15th
• 2016: November 7th

I don't think that's the problem, it's just too long to wait