This is an OLD matter- it's been bugging me for the past 261 chapters, but I've never got around to asking about it before (well not really, it was actually since the END of that plot arc, but whatever).
In chapter 103 (near the end of Naruto's duel with Neji) Kabuto treated Hinata when she started coughing up blood again. After stabilizing her, he made sure she would remain unconscious and subsequently knocked out Kiba.
This was one of the most important moments in the series for Hinata- Naruto had promised her -he'd sworn on her blood- that he'd defeat Neji both to avenge her and to vindicate her decision to fight her destiny. Then suddenly, just before Naruto turns the apparently hopeless battle around and produces one of his most stunning victories, she collapses and misses the whole thing. This is plain stupid if you ask me.
So my theory is that this was the groundwork for a plot development that Kishimoto abandoned. I believe that Kabuto's actions were a precursor to him kidnapping Hinata (either for Orochimaru or himself) in an attempt to gain the power of the Byakugan. As Neji was actually right in the middle of explaining during the scene, Hinata had been kidnapped once before for this very reason. It makes sense- there's no other reason Kabuto would have knocked out Kiba, since he would have been expecting him to be knocked out anyway by the mass-hypnosis genjutsu when the attack began. Kabuto's intended plan was most likely that after knocking out Kiba, he would steal Hinata away and return in time to take part in the attack. It was mostly likely opportunism on his part rather than a prepared plan -taking advantage of the fact that he had an excuse to remove Hinata from the crowd (to treat her)- all he had to do was disable Kiba and he could make a clean getaway.
This was probably a precursor to one of two possible plot developments. Either Hiashi (Hinata's father) would discover her being kidnapped and show his true feelings for his "useless" daughter by rescuing her, or she would actually be kidnapped, leading to a rescue plot arc, probably involving Naruto. Most likely Kishimoto gave up on the idea altogether, which is why he left Kabuto's actions after knocking out Kiba ambiguous- so he'd have the freedom to choose later on. He abandoned the first idea because he didn't want to write in ANOTHER serious story to the arc when he was already juggling the 3rd vs Orochimaru and Sasuke/Naruto vs Gaara (as well as Shino vs Kankuro and the 2 battling ninja armies), reducing Hiashi's part in the battle to just a cameo. Also, he'd given Hiashi a lot of character already when he came to apologize to Neji after his loss, so probably felt it was extraneous. The second possibility was abandoned as being difficult to work with (it would have meant hunting Orochimaru to his lair no less) as well as disrupting the story of the 3rd Hokage's funeral, carrying on the whole chuunin exam arc just a BIT too long (it was already the longest single arc in the entire story, a position it still retains) and develping Naruto and Hinata's relationship far too soon.
When Naruto, Hinata and Yamato were confronted by Kabuto in 356-357, I thought that maybe Kabuto had planted some kind of sleeper effect in Hinata's body when he treated her, which he was going to turn against them now (possibly to hold her hostage against Naruto), but he left without doing anything (or even giving Hinata a glance) leading me to discard this theory. So what do you guys think?
(Incidentally, did anyone notice that in 356 when Kabuto referred to Naruto as the kyuubi right in front of Hinata there was no reaction from her at all? Although Sakura appeared to already know about Naruto when he told her in 252, I doubt it had become common knowledge and Hinata was one of very few characters who had NEVER seen Naruto's kyuubi power due to missing his duel with Neji. Odd, very odd.)