Today's Dark Heresy day and I am not at all ashamed to say that I have done literally zero prep work. Partially, it's because I'm that kind of a guy; I would much rather go by the seat of my pants than prepare a bunch of stuff that probably isn't going to happen anyways, and partially because I front-loaded all of my work when the campaign was brand new and now there isn't hardly anything left to do except watch it unfold.
It's kind of a neat experience. I have a long list of plot elements to drop, events to unfurl, and ominous portents to unleash... but no preparation left. All I have to do is go over my notes, make myself a drink, and try and get back into the mood of the game. It's completely the opposite of the mood of the last couple of games (time shenanigans and high fantasy, respectively), but Dark Heresy has the added advantage of being the most suited for my personality.
Hopefully I don't mess things up. It's hard to get back into the groove like this.