Ok, I admit it. I am an achievement junkie. Though I would have to say that there are people out there that are a lot worse than I am. My achievements are growing, and I am working on a few specific ones.
I have a friend on Muradin who also has a blog Windfury Crits who just wrote about his love/hate relationship with achievements. I on the other hand LOVE them. I love the fact that there is something else for me to aspire to besides just raiding.
As we speak I am currently going back to all the old instances and completing them. I am trying to get eventually get the title of Salty - for completing all of the fishing achievements as well as getting Loremaster for finishing all the quests everywhere.
I find that I get bored doing one achievement, so then I just find another and try to do that one. It sometimes seems like a daunting task to work on some of them, but I enjoy it.