1) I love tactical movement! What a kick-ass little movement rule that more games need.

2) I'm watching John Carpenter's "The Thing" and thought, "Wow! What a deliciously evil creature to put into DH. Perhaps in a space hulk or lost colony. Maybe even a hive..."

The Thing from Another World is certainly an interesting critter, but, personally, it doesn't strike me as being quite right for Dark Heresy. Most of the tension in the movies comes from the guys at the arctic base not being unused to that sort of situation (and, thus, being extremely paranoid) and also being attached to and reliant on their fellows and being hesitant to kill anybody unless they absolutely had to. The most common portrayals of operatives in the 40k universe would have them not particularly freaked-out by the idea of a mimic/parasite-type alien (there are several existing species, like Tyranids) and might kill the suspected alien without much of a second thought. Or at least one of them would be fanatical enough to kill everyone (including themselves) just to be safe. Or they'd make their report and the Inquisitor would just declare Exterminatus and blow up whatever planet the thing was supposed to be on (or even his own ship, if he suspected it'd gotten that far).

I think if done right it is very 40Kish, espcially if all the characters are "civilians" and dont know squat of xenos and so forth.

I would set it in the lower decks of a huge starship and have the PCs all be pressganged within the last few years or so, so they are compentent enough to be assigned to "crew" some obscure isolated part of the ship but still not 100% masters of their location.

I think a scenario where the players distrusted each other enough to want to destroy one another, a planet or even commit suicide is right up the DH alley. You could award bonus xp if the players managed to eradicate the xeno menace without resorting to Exterminatus or burning down their fellow acolytes. Or you might even have a situation where a character is copied and a willing player may have a lot of fun trying to hide the fact that they really just want to escape to spread themselves as far as possible.

Callidon said:

You aught to get a small pile of note-cards with "Uninfected" written on them, and hand them out to each player. Tell them that one of them might be "infected." Let them know that there are several more cards than players, so there's a chance none of them are (and in fact, none of them are, meaning you didn't just kill a player for plot,) and watch the tension rise.

That's a very cool idea!

That it is! Some agile and lateral thinkers round here!