I was recently carousing through my local Borders and I picked up Creatures Anathema because it seemed to have some pretty interesting background information in it. I don't plan on every playing Dark Heresy, but I would consider picking up some of the expansions and maybe even the core rules if they had some pretty interesting and unique fluff in them (the whole idea of a techpriest taken over by virus controlled mechanical parts was particularly cool in Creatures). Does anyone else know if there is interesting snippets in the other books?