A couple of thoughts on the diary (since this is, of course, one of the areas to which I give the most attention :)):

Of course Tom enchanted the diary so that he can get his grip around the writer from the very beginning — in fact, it’s even possible that there might be a charm of some sort to make it enticing to a person even before it’s opened — almost a veela-effect, if you will, only it’s the book that is attractive. It’s a very potent, powerful object — one that I’m sure Malfoy had closely guarded away, with much caution. When Ginny writes in it, even for the first time, even those simple words “Dear Diary”, she is in essence beginning to bond herself to Tom — putting bits of herself into him, until he has the power to return the favor, so to speak.

I do agree that Tom is technically powerful enough to specifically exert force on Harry when he finds the diary, in order to ensure that he writes in it — after all, if Tom eventually gains enough of his own… “lifeforce”, I guess, to become an actual physical being of sorts — then surely by the time of Harry’s discovery of the diary, Tom is strong enough to influence him. BUT, I don’t think that he’s specifically influencing *Harry*. I don’t think that the diary is “conscious” by that time, actually — so the subtle power that Harry feels is one of two things (or, possibly more likely, a combination of them):

1. A charm, as mentioned above, that makes the book very enticing to whomever has it in his direct possession (my mind goes back to the book that Ron mentions, that you literally cannot stop reading).
2. The influence is actually just Tom’s normal “calling” that he has for Ginny Weasley — only since Harry hasn’t yet written in the diary, he feels it not as an irresitable urge, but as a weak pull on his consciousness.

In any case, I don’t think Tom is aware, before Harry writes his name in the book, that he is actually in Harry’s possession. Quotage:

“Imagine how angry I was when the next time my diary was opened, it was Ginny writing to me, not you…”

Even though Tom is a liar, I don’t believe he’s lying (or has reason to) here: He didn’t know who had picked him up and when — he’s only truly “conscious” when the diary is opened — at least at this stage of his, shall we say, literary growth and development.

I wonder if the diary had been found by anyone else, if he’d have floated up the words “Property of Ginny Weasley” in order to get back to Ginny’s hands?