Every April Fools' day it reminds me of my first 4/1 in the game industry. I had been working on Ultima Online for about six months and it was still run by Origin Systems in Austin, TX. The players had rose-colored glasses of the era of UO that came with the first expansion (The Second Age) just prior to the second expansion (Renaissance). There was always a post on the forums calling for a pre-Renaissance server.
So on April Fools' I decided to give them just that. I tweaked some flags on the test server to turn on the much more difficult "Siege Perilous" ruleset and renamed it "UO Pre-Ren".
I wish I still had a link to the post on the forums with the player responses after that.
In retrospect, while it may seem a little mean, it was well within the spirit of the holiday. And you've just got to expect stuff like that on April Fools' day.
And, in case you're wondering what we did in EQ2, Kendricke found it by surprise.
ALSO: I just checked the Rock Band song list to see if there were any new songs worth downloading. At first I thought the new song was just an April Fools' joke, but it's for real! I'm jammin' away on it right now! Best of all, it's free!