Parallels, Shipping, and Betrayal
I am primarily a trio shipper; by that I mean I enjoy reading and writing fics about various pairings of Harry, Ron, and Hermione. However, as far as reading goes, I will read pretty much any ship, even if I don't 'ship' it - with two exceptions: Harry/Ginny and Draco/Hermione. I tried to sit down and think about why I absolutely cannot read these two ships, and I think it's because they bother me on a very deep level. Draco/Hermione isn't a pairing I run across often, so I don't have any clear thoughts on it right now, but I do have plenty of thoughts on Harry/Ginny.
Part I - Why Harry/Ginny bothers me
Some rabid anti-Harry/Ginny shippers have said that they could tolerate a Harry/Ginny ship better after OP than they could before. I dislike it even more now than I did before. In my mind, Harry/Ginny sends a clear message to girls that "if you pine over a boy long enough, he'll eventually love you." I can't express how disturbing this is to me. Even though Ginny appears to have moved on in OP, I can remember many a crush I had on a boy at her age, and if said boy had decided to show interest in me, I'd have been hard-pressed to turn him down. Tarie brought up a good point in a conversation regarding this; Harry suddenly noticing Ginny now that she has moved on is actually quite demeaning to Ginny - it's like Ron's "oh, Neville's right, you are a girl!" comment to Hermione in GF22 but more hurtful as Harry is older at this point, with a little more experience with girls under his belt, and should know a bit better.
If JKR had shown Harry and Ginny developing an actual friendship, instead of him only knowing her as 'Ron's little sister', then I might view it differently. She's set up Harry and Hermione, or Ron and Hermione, or other possibilities, if you want to go there, as developing very close friendship with the potential to develop into more. But with Harry and Ginny, there has been infinitesimal development, and the final two books of a seven book series is simply not enough time to develop it. It took three books to resolve Harry's crush on Cho, for example. There have been plenty of opportunities for JKR to develop a friendship between Harry and Ginny. They are in the same House, Harry stays at her house a great deal in the summer, and they both like Quidditch. I actually found it very hard to swallow that Harry's known her all this time and not known that she likes and is good at Quidditch. Have they not had impromptu Quidditch games at the Burrow before?
The other thing that bothers me is the events in the Chamber of Secrets. Harry (nor anyone else as far as I can tell, but that's another story in itself) has ever given a second thought to Ginny's experience in the Chamber save for a brief mention in OP when Harry was feeling sorry for himself. We all know that Harry's extremely self-centered, (and to me, that's understandable given that he hasn't been raised in an environment where he would learn to have any sort of empathy for the feelings of another), but for him never to consider the effect of Ginny's possession by his nemesis is ridiculous. Perhaps JKR is deliberately avoiding them discussing this so that they can bond over it later, but this seems contrived that they never talked about it at the time it happens. I find it extremely unlikely that a boy would fight a giant snake and destroy a possessed diary, almost dying in the process, to save his best friend's sister, and then never say a word about it to her or to either of his best friends. Not a single word. In later books, it is almost as if the events of book two never even happened. Harry almost never thinks about those events unless someone else brings them up first.
Not only that, but Ginny never approaches Harry to say "Hey, thanks for saving my life. You almost got killed down there, and I appreciate you sticking out your neck for me." Of course she wouldn't have done that right away, but at some point in the following three years there could have been a moment for that. She could have even sent him a note! And surely the spunky, outgoing, self-confident Ginny we saw in OP would have no problem saying such a thing to Harry even if he was being a moody punk. It's almost as if she takes his rescue of her for granted. I find it incredibly hard to believe that they could go through such a dramatic, life-changing experience and not speak of it to each other for over two years.
When the subject of the diary is finally brought up in OP, it is skimmed by with such carelessness that I almost missed it. If JKR is setting up a Harry/Ginny relationship, she missed a tremendous opportunity for it in OP23. The part where Ginny snaps at Harry - "Well, that was a bit stupid of you," said Ginny angrily, "seeing as how you don't know anyone but me who's been possessed by You-Know-Who, and I can tell you how it feels." - lasts for less than a page. Harry still hardly thinks about her experience at all. He doesn't really reflect on it; he simply has his typical 'oh' reaction and moves on. This would have been the perfect time to have Ginny make some sort of comment that changes Harry's attitude or mood slightly, foreshadowing some future relationship development, but not a thing.
Given this, I feel that if JKR is truly going for a Harry/Ginny relationship, she has set it up very poorly. Harry is the main focus of this series, and whoever his eventual love interest may be, it should be someone who is developed at least as much as his best friends are. Ginny has not been developed in that manner. This leads me to wonder - if Ginny's purpose is not 'hero's love interest', then what is her purpose other than 'hero's best friend's sister?'
Part II - What I think Ginny's real role in the series is
To me, there is an odd and disturbing parallel between MWPP and the Trio+Ginny. The Trio doesn't include Ginny in their expeditions (save OP, and then only reluctantly), Harry doesn't confide in Ginny the way he confides in Ron and Hermione, and he doesn't think of her near as often as he does Ron and Hermione. Think of how Peter was described by the teachers in the Three Broomsticks in PA10 - as a tagalong. He was their friend, but he wasn't as much a part of the group as Remus, Sirius, and James were. They trusted him enough to include him in the Animagus transformation, but obviously had little respect for him, considering their actions in the Pensieve scene in OP. Ginny is Harry, Ron, and Hermione's friend - apparently very close to Hermione though we've not really seen this until OP - but Ron and Harry hardly give her the time of day. Ron only seems to pay attention to her when it concerns her choice of boyfriends or Yule Ball dates.
If you wanted to draw a parallel between the two generations, keeping in mind that any generational parallels are imperfect, you could do it as such:
Compare these passages from CS and OP28 (keeping in mind the age differences at the time):
(CS3) - "Ginny," said Ron in an undertone to Harry. "My sister. She's been talking about you all summer."
"Yeah, she'll be wanting your autograph, Harry," Fred said with a grin, but he caught his mother's eye and bent his face over his plate without another word.
(CS3) - "Ginny," said Ron. "You don't know how weird it is for her to be this shy. She never shuts up normally--"
(OP28) "Put that away, will you? said Sirius finally, as James made a fine catch and Wormtail let out a cheer. "Before Wormtail wets himself from excitement."
(CS4) - The moment she saw Harry, Ginny accidentally knocked her porridge bowl to the floor with a loud clatter. Ginny seemed very prone to knocking things over whenever Harry entered a room. She dived under the table to retrieve the bowl and emerged with her face glowing like the setting sun. Pretending he hadn't noticed this, Harry sat down and took the toast Mrs Weasley offered him.
(OP28, pg 644) - James was still playing with the Snitch, letting it zoom farther and farther away, almost escaping but always grabbed at the last second. Wormtail was watching him with his mouth open. Every time James made a particularly difficult catch, Wormtail gasped and applauded.
I've also seen people slot Percy in this role, but in my opinion Percy is too obvious a choice for the traitor role. I believe Percy is a red herring, both because he is obvious and also because he isn't close enough to Harry (or his family either at this point) to know anything of use to Voldemort - and that it will be Ginny who ultimately betrays Harry for whatever reason. She is close enough to Harry and her Order-involved family members to actually have somewhat useful information. This cannot be said about Luna or Neville, the only other cohort characters that Harry seems to trust. In addition, the only possible reason that I can see for JKR delaying any sort of resolution of the events of book two is if Ginny is harboring some residual resentment - perhaps she is angry and resentful that no one has seemed to care about her experience with Tom Riddle and the diary (and rightly so). She could also be resentful of the fact that while she and Hermione appear to be close, Hermione seems to be closer to Harry and Ron. Harry, the boy she's crushed on for years, and Ron, the brother closest in age to her, both of whom constantly brush her off and tell her to go away.
You could expand this further with a Snape - Draco parallel, and also Lily - Luna or Lily - Neville, but that's a bit blurry and I'm not sure how that would quite play out. We don't really know enough about Luna at this point to know what her purpose is; it's possible that we'll learn about another MWPP-era character that will give us more insight into events in that generation. We also need to know more about why Snape turned against Voldemort, and why Peter turned against James and Lily, but I do feel that JKR is drawing a very clear parallel between the two generations, and if there is a betrayer in one, there must be a betrayer in another.