I just wanted to say, i have recently finished re-reading Half-Blood Prince, and i am no longer a believer in the Love Potion Theory.
The theory was that Hermione dosed Harry up with Love Potion in order to get Harry infatuated with Ginny. With so many references to Love Potion throughout the sixth book, it seemed likely there was something more going on than was immediately obvious, and i was so disgusted by the 'clawing monster' in Harry's chest that i was eager to leap at any explanation other than the apparent one.
I've been re-reading the entire series actually (since November - i am a slow reader!) and when i came to Half-Blood Prince i decided to look especially closely at how Harry behaved around Ginny, whether there were any odd signs, and whether there were any chances for Hermione to slip Harry some potion. Unfortunately the evidence was not conclusive. Whilst there are a few signs, i don't believe there are enough for JKR to turn around and go, "Haha! It was Love Potion all along!" Jo is an extremely talented author who can hide things, yet make them seem glaringly obvious once you know they are there. That's just not the case with this theory. There need to be a few more *slap your forehead* moments where you know you should have realised what was happening.
The theory starts well. It begins at The Burrow, where Hermione has been for a few days before Harry arrives. There are suspicious flowers to cover up the smell of gunpowder, and that hard sweet in Harry's pillowcase. I do not believe Mrs Weasley would allow Harry to sleep in a room full of gunpowder, nor do i think Mrs Weasley would overlook a sweet in a pillowcase, having prepared the room for Harry. The flowers, of course, are claimed to be linked to the smell of Love Potion for Harry; not actually the smell of Ginny, but a particular smell that has been designed for Harry to associate with Ginny in an amorous way. We also see Harry waking up feeling drugged and drowsy, and Hermione's anxious command that Ron not hit Harry. For that whole scene, Hermione is casting sideways looks at Harry.
I would actually say that this Burrow scene (pages 87-89) is the strongest scene in the book for supporting the Love Potion theory. There's definitely plenty to get my suspicions up. So i continued reading, convinced that there was plenty more proof to come. We get a bit of Harry-Ginny interaction, but really not much to speak of. The theory claims at this point that Hermione has been trying out a self-concocted Love Potion and now assumes it hasn't worked. (Harry, of course, is expert at resisting the Imperius Curse so a Love Potion should be easy to resist!) Hence Hermione's interest in Fred and George's Love Potions at Diagon Alley.
Another plausible scene is the first trip to Hogsmeade (pages 228-233). Before the trip Harry has no reaction to Ginny going with Dean. Then Hermione buys a round of Butterbeer. It clearly states in the book that harry *drains* the Butterbeer, and then scowls, thinking of Ginny and Dean. Now, if there were a few more scenes like this when we could see a clear opportunity for Hermione to spike Harry's drinks, i would be completely sold on the Love Potion theory, Unfortunately, this is the only one, and to be honest, Harry's mood change seems rather coincidental. I mean, it's only a scowl. The birth of the clawing monster does not arrive for another 30 pages, on a totally different day.
If there's any pattern i can find, it's Quidditch. Harry's monster moments seem closely related to Quidditch tension, which makes perfect sense, really, when emotions are running high. Sure, there are periods where Harry appears completely oblivious to Ginny, but i must remember that Harry is sixteen at this point, and can't really be expected to have consistent emotions when it comes to love. The funniest thing is, whenever Harry pays no attention to Ginny, it's usually because Harry's preoccupied with what Draco is doing! There's a good one for the Harry/Draco fans! ;)
Anyway, it's not as if Harry stops thinking about Ginny altogether for long periods of time. There's even an acknowledgement on page 286 that Ginny has been cropping up in Harry's dreams, but Harry's trying not to think too much about them, or about Ginny. So that tells me that Harry is in fact in control of these emotions; it's not Love Potion controlling Harry. The times when the monster appears (there's actually only three of them in the whole book) i guess Harry just lost a bit of that impressive self-control for a moment.
So Hermione confounded McLaggen and justified tweaking the circumstances. So Hermione knows a lot about how to smuggle Love Potions in. So Hermione doesn't think Love Potions are Dark or dangerous. So Hermione had a smug look when catching Harry looking at Ginny. It's all just coincidental. These coincidences would be great if there was a bit more non-coincidental evidence to back it up, but i really don't think there is.
Finally, i discovered there is a third reference to the flowery scent, and it's right at the end of the book. It's Ginny pulling Harry away from Dumbledore's body. The flowery scent tells Harry that it's Ginny. This is at a moment of intense grief. I really don't think Love Potion is going to be doing anything much for Harry at that moment. So i conclude that the flowery smell is in fact real; Ginny really does smell of flowers - it's not just Love Potion creating that smell to arouse Harry.
So there it is. I posted a few months ago when i thought Love Potion might play a part in Deathly Hallows, and i wanted to be able to go "Ha! I told you so!" if it did. Now i'm posting to say, i really don't think it's likely, and i no longer believe the theory.
Crap! This means that i have to accept that Harry is genuinely in love with Ginny! Noooooooo!!!!