Enough rant. Here are a couple rules verifications you should know when facing or playing Grey Knights.
Hammerhand.
Does this stack when it is used twice in a single unit. For example, a librarian and the unit he is attached to use it?
Yes, this one was done correctly by my opponent, but I want to make sure others out there realize this. Here is the FAQ quote on the main rulebook.
Q: Do the effects of the same psychic power cast multiple times on the same unit stack? (p50)
A: Yes, unless specifically stated otherwise
Multiple Assaults
This one did not effect the game in any way, but was brought up afterwards, when my opponent claimed "Multiple Assaults must be declared"
This one is simply not true. There is nowhere in the rulebook nor faqs that says this. When you plan on multi-assaulting, you must only declare the primary target of your assault. Then once you engage that target you may multi-assault as you wish. Most people normally tell their opponent that they are attempting to multi-assault as they are doing it. That is how it works.
Nemesis Force Staves
This one did effect my game, as my opponent declared incorrectly that a nemesis force weapon gave his librarian a 2+ invul save against everything as long as it was in the assault phase. This is not true. The FAQ ruling simply allows that someone wielding a nemesis force stave, can take its 2+ invul save to anything while it is engaged. This means that charging through dangerous terrain does not allow you to take your 2+ invul save. Here is the FAQ ruling.
Q: Can the save granted by a Nemesis warding stave be taken against all Wounds suffered whilst the wielder is engaged in close combat and not only against Wounds caused by close combat attacks? (p54)
A: Yes.