Here are several rules from last Sat game.
Deathwing Vehicles, 6th ed Dark Angels Codex pg 40
A Deathwing Vehicle has the Preferred Enemy (Chaos Space Marines) special rule, and if a Deathwing Vehicle suffers a penetrating hit, you can make your opponent re-roll the result on the Vehicle Damage table. You must accept the second roll, even if it is worse than the first.
Context: Shawn mentioned that Deathwing Vehicles have venerable that allows damage result to be re-rolled.
Turning Vehicle after Disembarking, Disembarking 40k6, pg 79.
If the vehicle had already moved before the unit disembarked, the vehicle cannot move further (including pivoting on the spot) that turn.
Context: Assault Terminators disembarked Land Raider Crusader after it moved. Wanted it to turn to shoot a Leman Russ. Shawn and I looked it up and vehicles can't pivot once a unit has disembarked from it.
Going to Ground 40k6 pg 18
A unit that has gone to ground cannot move, Run or charge, it can only fire Snap Shots when it wishes to shoot, and can fire Overwatch. At the end of its following turn, the unit returns to normal, the marker is removed and the unit is free to act as normal from then on.
Context: Shawn's Veterans went to ground for 6+ cover save against Land Raider shooting. Thought they stood back up after his shooting phase. Shawn reminded me that it is only after the end of his turn.