Beyond the utterly amazing Youtube prank this year, which I suspect anyone who's reading this has already seen...
xkcd is now Questionable Content
Questionable Content is now Dinosaur Comics
Dinosaur Comics is now xlcd
Also, Google wants to make a
Mars base for us to live on, plus you can take a test to see if you have the right stuff. My dislike of backgammon probably caused me some trouble there.
WoTC's D&D site is
amazingly funny though because everyone knows Halflings aren't real people. Also, Gnomes are back.
So far, no other pranks yet today that I have seen.