If you use Plague Marines in 7th, it's worth noting that Defensive Grenades no longer give you Stealth within 8" of the unit shooting at you - they still negate the attacks bonus for charging, but they may now be thrown as a 8" range, Str1 AP- Blast with the Blind special rule. This can be really nice for softening up a low-initiative target such as Ork Boyz before you charge (if you Blind a squad of Ork Boyz and then you charge them rather than vice versa, they need 5s to hit and 6s to wound!).
It's also important that if your strength is equal to your opponent's toughness, you don't get to re-roll your To Wound dice for Poison - only if your Strength is higher. This is a pretty major hit to Genestealers and the like who were using Poison to give themselves Shred against T4 targets, but that's the way it is now I'm afraid.