Here's a post from 3.14 '08:
I was so wrapped up in the BSC** conference call that I almost forgot the important stuff.
Some have dated the first Pi day celebration to March 14, 1592 at 6:53:58. This is incorrect.
It is obvious the Druids knew Pi: 

Coincidence? I think not.
Some folks go further back:
The Great Pyramid and the Pi Factor
Here's the Pi song.
Here's a slice of Pi:
3.1415926535 8979323846 2643383279 5028841971
Here's Kate Bush's Pi song.
PiemanReal name: Homer J. Simpson
Occupation: Pastry VigilanteQuote: "Don't do the crime if you can't do the key lime!"
"Apu: In fact I can recite pi to 40000 places. The last digit is one!
Homer: Mmmm, pie."
(episode [9F21] Pi (Pie) {sbj})
*Here's the Hamm's Bear pie commercial
* 
Blueberry Bear with Vally Lafamme and winners of Blueberry Pie Eating Contest. ..
*The Yogi Bear Show, "Pie Pirates"
**Blueberry Pi
And Science Museums:
Welcome to The Exploratorium's
2008 20th Annual Pi Day Celebration page
(Here's the Exploratorium's 2012
Pi Day page)
From Wikihow:
How to Celebrate Pi Day

How old are you in
Pi years? Happy Pi Day
