Lunar Festival 2011, or "Where are the Elders!"

A few elders have moved around, such as Stormwind's Elder being placed out front of the city (the game tells you to go to the destroyed park, but it's wrong).

Lunar Festival 2010, 2009, 2008, 2007.

Pick up the Lunar Festival quest.  Head to your Alliance or Horde Harbinger.  Pick up the quest to shoot off rockets.  Get 8 rockets (any color), 10 [Red Rocket Clusters], and 10 [Firecrackers].  Keybind the [Red Rocket Cluster] and shoot off all 10 as fast as you can to get an achievement.  Repeat with [Firecracker] for another achievement.

Grab your invitation, use it in the column of moonlight, go here and get the Omen quest.  Head for this spot and look for a group killing Omen (if you do this in the first day, he is always being downed -- later in the week is much harder).  Help if you can.  You want to stand in him while he's dead, it doesn't matter if you helped kill him.  Turning in the quest with the buff on you from his corpse (dying removes it) gets another achievement.

Elder Time

There's a list here, but it's not 100% accurate for Cataclysm yet.  I'm sure it will be fixed by the end of the week, but here's a good rule of thumb: if you can't find an elder where it's supposed to be, go to wowhead and search for the elder's name (given in the wowwiki listing).  Under the Comments tab, go to the most recent comments and glance over them for the elder's new position.  You will always find the answer there.

If only coordinates are given and you don't use coordinates, go to Tools > Maps and select the area you're in.  As you hover over the map, it will give you coordinates and you'll be able to see where on the map your elder is.  :)

After Getting All Elders

Buy clothes with your tokens.

You're an elder now!