Ok.....Harry and Luna did have that whole mistletoe thing...but Harry pretty well much dismissed it, b/c then he wasn't thinking of her like that and I think Luna...being dreamy...was kinda being funny/flirty/loony b/c that is her character. You could be under mistletoe with a good guy friend and give him a kiss on the cheek...its just the thing to do. With her so dreamily all the time, of course she would be into something like that.
As for Luna, it was PRETTY obvious for her wanting to be near Ron from the VERY beginning when we were introduced to her character. Other than reading hte quibbler upside down the 1st thing she wanted to do was to help Ron with his things off the train. She didn't ask Harry...She asked Ron. AND if she wanted to be closer to HArry then she would have accepted his offer to help her find her things at the end of book 5. She said no, they always come up somehow. Now i do admit that i had thought about the fact that she could be a possibility for Harry...he did change towards her, but Harry is also goign to look at his friends, Hermy, Ron and Ginny (yes she is still a friend). Hermy of course doesn't like her and she is one of Harry's closest friends aside of Ron. NEville is scared of her........so you see...he doesn't really have the support from his friends. The reason he felt better at the end of book 5 from talking to her about the Veil is b/c he so DESPERATELY wants to contact Sirius again and YES she is a person who can help him and he will admire her for this....but I dont see her liking him in that way. AND I think if for some reason all of this shows in book 6 then there will be more ginny too. Ron is goign to oppose luna, b/c he wants Harry with Ginny. Hermy doesn't like her, b/c they are too different and there was that whole library scene that when Harry was in that --im pissed off at everyone who isn't going through what i am-- mood...well Ginny was there and she calmed him down AND she did give him the Snitch on Easter. I don't remember Luna giving him anything, except for an interview from Rita that went into the Quibbler. Which was a HUGE thing for Harry.......but Luna and Harry have no past. Harry can talk to her about death b/c her mother had died. He needed to talk to someone who had been through what he had been, so it wouldn't seem like everyone else, who is always trying to prod. I do think Luna and Harry will become very good friends, but I do think JKR will kill her off.
I think with Voldemort growing fonder of how Harry thinks and feels he will catch on to someone close to him. Yes Luna is this person FOR NOW, b/c she can help him contact Sirius and I think that Voldemort might try to take her to hurt Harry. This is why I think her character will die off. I mean we heard about Diggory's parents and stuff and he still died off....I say that b/c we hear about Luna's dad who works for the Quibbler. I do think that Luna will give him LOADS of info.....but he's not going to be interested in her......he's goign to be interested in how to find Sirius. AND remember....Luna found out about Sirius from Ginny!!!