1: How long have you been in the hobby?
Myself, about six or seven years now. I started with 4th ed.
2: How important is Fluff to you, relative to other aspects of the hobby?
It is definitely my favourite aspect, it shapes everything else I do.
3: How devoted are you to the works of the Black Library? By this I basically mean what compels you to buy/read one of their novels, do you pick them because of the races involved, follow certain serials, on a whim, etc...
I choose a novel or other work based mainly on the characters involved. I followed the entire UM, Cain, Eisenhorn, Ravenor and DoW series right through. I own about two dozen novels, but have read much more, including CV and the heresy novels, several compilations and of course, the odd fanfic here or there.
4: How many codexes have you taken the time to read thoroughly, including older editions?
Everything from 4th ed onwards. A few older works that people have been kind enough to lend me.
5: Do you enjoy postiulating theories, pondering mysteries, and writing your own works to expand your enjoyment of the hobby?
You know I do.
6: If you have anything further to add, feel free.
I think I did alright.
EDIT: 7: My area of expertise would be alien fluff. Particularly Necron and Tyranid, but I would consider myself well versed in the backgrounds of orks, tau and eldar as well. Knowledge of Dark Eldar witheld until new dex is read properly. Currently have only read it once and not completely.
My knowledge of the Imperium and Chaos is secondary, but I still know enough to put pretty much all my local GW staffers to shame.
EDIT: 8: My weakness is probably the Imperium, but especially the non military side of the Imperium. I don`t know all the facts regarding the Inquisition, I couldn`t tell you much about an imperial civilian`s life, but I do have a decent general knowledge regarding most astartes chapters/legions and IG regiments.