In my opinion? TRAINWRECK SYNDROME. For me, at least. It started to bore me and really drag on OotP forward, and yet for some reason, I still bought Deathly Hallows, and I still read it ASAP (although not with as much vigor as I could have). It bores me to death now, and I couldn't look away from it.
12
Damn it, Rowling. DX