About the locket not being shown in the movie:
I know JKR works with the filmmakers. In OotP, she requested that Kreacher be left in the movie as he was very important later on. But the thing is, what did Kreacher do in the OotP movie. In the book, it was notable to have him because of the locket. They were throwing stuff out and Kreacher saved it. Later, Mundungus stole everything he could on top of that. Who knows where that locket is now. The locket is definitely a horcrux and is definitely the one they were looking for at the end of HBP.
I imagine that in DH, it will just suddenly dawn on one of the trio that "Hey, that frickin locket is the one we are looking for!" Since it was completely left out of the 5th movie AND they don't go to Sirius' house during the 6th book, how can they possibly explain this when it happens in the 7th movie. The only explanation I can think of is that perhaps the 'ol switcher-roo that Regulus did will not happen and Dumbledore will in fact get the actual horcrux at the end of the 6th movie. But then why include Kreacher in the 5th movie if his only job in the 7th book is to advance the locket sub-plot.
Thats my main complaint about the 5th movie. It left out so much of the little plot details that will have to be re-arranged or redone in the sixth movie when they could have been covered in the fifth easy. It's just a lot of little things that build up that even some fans missed. Several people in this thread knew nothing of the locket in the 5th book. My friend, who has read the books several times also forgot about it. Maybe the the screenwriter and JKR forgot about it.
Another thing that irritated me in the 5th movie was teh lack of the handheld mirror Sirius gives Harry. It explains in the book how the order wound up at the Ministry to defend Harry. It also accounts for the whole "Sirius' death was my fault" sub-plot of Harry.
Now, following the line about JKR working with the filmmakers and people thinking Neville is important. I used to think Neville was important too. I mean, the prophecy could have applied to either of them. I think people are hyping up Neville but almost his entire backstory was left out of the 5th movie so I think that subplot is going nowhere. In fact, JKR said in a interview that although it's interesting to consider what might have been if Voldemort chose Neville, it was not important to the story line.
One more thing about JKR's involvement in the movies. I remember that Alfonso wanted to put in little people dancing on the piano in one scene basically playing the piano. JKR overruled it stating that something like that doesn't exist in her world. I was just thinking, what about the yard gnomes. I believe it's the 4th book that Harry goes to stay at the burrow and the pull yard gnomes out of their garden and fling them far away. Why could they have done the dancing on the piano? (completely off-topic but I just thought of it the other day)