I have started documenting everything I know about my job. I am writing this as a book in docbook format. Some developers horde information as job security. They don't want new people to learn what's going on, so they can maintain their status.

I have a different perspecitive. If you are the only person that knows about system X and then you get an opportunity to work on system Y, they might hold you back, becuase you are the only one that can maintain and develop system X. If you have documented X and shared your knowledge freely, then anyone can step up and take over X while you get to do the really fun new stuff.