1: How long have you been in the hobby?
I have been in and out of the hobby for years, only very recently back in. I spent a solid few years regularly involved with these forums in particular, and with the hobby IRL.
2: How important is Fluff to you, relative to other aspects of the hobby?
Fluff is most of the hobby for me. I don't get to play as often as I'd like, and I paint only sporadically.
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 follow Gaunt, Cain, and have read all of the Last chancers. I'm veeery far behind, though. If a Black Library book falls into my lap I will read it, but I will only spend money on it if it involves the Guard.
4: How many codexes have you taken the time to read thoroughly, including older editions?
I've read through the two most recent guard dex's, the ork's dex, the former Which hunter Dex, the current CSM dex, current Grey Knights, and a Chaos Codex that I don't remember the age of, it was old enough to include cards and little tokens and such. I've also read the third BRB thoroughly.
5: Do you enjoy postiulating theories, pondering mysteries, and writing your own works to expand your enjoyment of the hobby?
Yes to all. The Star Child is my pet theory. I have an ongoing narrative in my head about the return of the primarchs and the emperor as well as the ensuing chaos gambits and galaxy shattering mayhem that would follow, and I someday hope to get it all on paper, but it's long and I am often preoccupied.
EDIT: 7: What would you call your area of expertise?
Pre-Imperial human history, and the nature of the star child are probably where I stand out the most. I've got quite a bit of knowledge about the Guard, it's organisation, it's trivia, etc, but no more than the average veteran Guard player.
EDIT8: What would you say is your weakest area of fluff knowledge?
My weakest area is probably the Tau, and space marines internal goings on, as well as anything that has been ret-conned or come to light in the past year or two.