1: How long have you been in the hobby?
Tabletop? Since 2010
But I have taken an interest at the beginning of 2004, before Dawn of War was released. Since then, I've played all the DoW games on the PC, read two dozen novels, and played an IG captain in a role-playing game. I only got into the tabletop recently because I finally managed to find three other guys who would play with me. I don't particularly like the idea of blindly rushing into an unknown bunch of people saying "Hey, guys! I don't know you, and you don't know me, but I wanna play Warhammer 40k!"
2: How important is Fluff to you, relative to other aspects of the hobby?
It's quite important.. Until recently, fluff was to me the most important thing in 40k, but playing and painting trumped that. Actually, painting trumped that, it's been consuming most of my free time, mainly because I'm slow (I can do a trio of guardsmen in two hours).
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 first picked up what was heavily recommended by the WH40k enthusiasts over at the relicnews forums. I started off with the Horus Heresy novels, and I think that is the best start anyone can get at the WH40k fluff for two reasons. One, it covers one of the most important events in the history of the 40k universe. Two, the series is a showcase for the skill and style of (almost) every Black Library writer, and that's great for picking out what you like. I liked Abnett's style immediately, so I picked up Gaunt's Ghosts, which I finally finished only recently because I insisted on buying only the omnibus editions.
Basically, I'll read a book if it's from an author I know to be good, or if it recieved good reviews, or if it's part of a series that I'm following. If a book doesn't satisfy any of these parameters, it might still be picked up if I have time to kill.
4: How many codexes have you taken the time to read thoroughly, including older editions?
Six of them. Imperial Guard, which is my own army, and has been a great companion for the daily doing of the Emperor (that's a reference to taking a shit). I also borrowed the current Space Marines, Eldar, Chaos Space Marines and Orks dexes from the friends in my gaming group, and I've read the .pdf Daemonhunters as well.
5: Do you enjoy postiulating theories, pondering mysteries, and writing your own works to expand your enjoyment of the hobby?
Yes, immensely. I'm border-line obsessively creative when it comes to these things.
6: If you have anything further to add, feel free.
I really like Warhammer 40k. It's my second favorite Sci-Fi universe (with the first one being my own, ofcourse).