Pirates hold a special place in my heart for many reasons (i.e.Captain Jack Sparrow, my guild name, etc.) And apparently the same is true of Blizzard as well: September 19 is Pirate Day. Go check your in game calendar if you don't believe me.
Coinciding with the annual Talk Like a Pirate Day, it's unclear what the day's festivities will entail exactly, tho there is a new achievement for carousing with pirates: The Captain's Booty. So save up your rum...and get your pirate costume ready....ARRRRRR Mateys.
P.S. Landlubbers should brush up on their pirate lingo over the next month.
9/19 UPDATE: Talk to a pirate in any capital city (sadly, none in Dalaran) for a 60 minute pirate costume to get youself in the mood.