That's December 11th 2004, and that was the day the Ciddies Revelations Thread was on. Also notable is July 26th 2004, when the Eyesonia thread began. 26th June 2004 was the mid-year Ciddies Revelations Thread. Trying to figure out what happened on Feb 5th... ah, it was the beginning of the EoFF Elections. 24th-26th March 2005 was heavily boosted by the up'n'coming April Fools. The Staff thread, of course, was duplicated so all those posts will count as double. Around 250-300 of the 1040 posts in that thread were made during those days, along with all the 'drama' posts throughout Feedback. Not sure on what happened during November 27th and 28th 2004, though!

EDIT: 5th December was RSL Day. May 24th was Something Awful's doing.

EDIT: Oh, Feb 5th was the beginning of the EoFF Elections, I was looking at the wrong Elections thread.