I've been thinking about Orochimaru pretty heavily for the past, like, two months--in anime club, we're watching the arc with the Gaara-Naruto and the Orochimaru-Sarutobi fights (and, man, if there's anything I want to see more of, it's Orochimaru-Sarutobi interaction). So, correct me if I've contradicted something in canon or forgotten to take something into account (& argue if you don't agree, :D); this is all how I know the guy.
Orochimaru understands goals, and achieving them, but he doesn't understand secrets so much as he understands that risk is different from suicide--that some things must be concealed if one wants to get anywhere with them. He certainly doesn't understand purpose in the way that Kabuto does (and has since childhood). He doesn't get hiding, the building up of oneself in secret; he doesn't really understand patience (because he only ever seems to be patient when he knows, for sure, that he will get what he wants), or carefully constructed plans from which one never wavers.
And, actually, I don't think that he has to understand purpose, or plans, or patience: his mind doesn't build on a solid foundation of knowledge and causality, etc., but works in intuitive leaps. He is a genius where Kabuto is merely brilliantly, precociously competent. The risks he takes are not the logical conclusion of a progression of steps, not some sort of conclusion he's come to after weighing the consequences, positive and negative; they come from something else, something unknowable, whatever the spark is that makes someone more than everyone else. There is no volume of information that would allow Kabuto to replicate Orochimaru's intuition.
I think Kabuto knows it, too. I think he does understand that Orochimaru has something that most people don't, whatever side they happen to be on. He's smart enough to use that. And, unlike the rest of Sound, he's smart enough to pretend that he's not. (I don't think he fools Orochimaru with that. He might not even intend to. But, strange as it is, I think that Orochimaru appreciates the pretense. Maybe he even sees it as proof that Kabuto cares for him, whereas he knows that pretty much no one else in Sound does. Certainly no one else in Sound both cares about and understands him, or even his goals. Unless someone wants to argue that Kimimaro had a clear picture of Orochimaru? :D)
I don't think that that knowledge that no one else cares about him is why Orochimaru's so coldly able to kill his subordinates, though. I think he just doesn't care about them. There will always be more people out there willing to do what he says in return for whatever favour he says he'll do them, or maybe just because they sense that he's both strong and dangerous. They're not irreplaceable, they're often not more useful alive than dead. They're not even particularly interesting, which might be a worse sin. Kabuto, whatever he might be, will probably always interest Orochimaru. (I'd even say that Orochimaru would keep Kabuto around if he absolutely knew that Kabuto would kill him one day, for at least two reasons: he'd want to know how he'd try to go about it, and he wouldn't believe that Kabuto has the skills (or, maybe, the balls) to manage it. He does have a tendency to underestimate nearly everyone, himself included.) And, also, I think that Orochimaru has always known that other people think that the stuff he doesn't think twice about doing is despicable, but he doesn't care about that, either. That sort of morality doesn't really apply to him.
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About Polyjuice, I wonder how exactly it works: do you turn into them as you are now, or as they were at the time of the hair collection? (We can pretty confidently rule out "as they would be at the age you are now", I think, given what we've seen in canon.) Is there a limited period of use for the hair, if it's to keep its properties? That is, can I cut off all of your hair now and use it over the next fifty years, or will the magic in the hair that lets me change into you wear off after a decade or so? What makes more sense? And was it ever actually stated somewhere that it had to be hair, or am I remembering fanfiction conventions instead of canon? :D