Or as it's known in my house... The Oracle.
But that's only because my Daughter just finished watching the Matrix movies and they (her and my Wife) see me with this book all the time, making notes on stuff and looking through it for the answers.
My Wife opened it the other day and simply stated, "I don't know what a single thing is in here," and put it back down.
Somebody posted their sketchbook a while ago and I've been meaning to post mine too. You see how fast I am with keeping up with the crowd.
This is really the only way I can keep track of everything I have going on with commissions and all the cool 40k stuff I find. I try to make notes on things I want to use at some point. Maybe it's a cool basing idea or somebody does a conversion that I want to copy, whatever it is, it goes in here for later use.
I keep track of my monthly painting points too (36 points for May for those interested) and money. That way I can show my Wife that "little men" makes money and doesn't just spend it.