I've had a theory for a while... and now I read something on mugglenet.com that kinda confirms it for me. It's not huge, but it's something as to what may happen in the 6th book (which is rumored to be scheduled for this January *squee*. See the front page of http://www.mugglenet.com). Anyways, I've always thought that Narcissa Malfoy would play some sort of role in the books, but I wasn't quite sure as to what. But after Sirius went on vacation, I realized what it may be. Sirius was supposed to be the last remaining Black, right? Well... now that he's indisposed, who gets Grimmauld place? I doubt he had made up a will... it's not like he held a lot of value for his family herilooms and I don't think that he's the kind of person who would make up a will. And Dumbledore said that Kreacher saw Narcissa as the last Black he had any respect for, which says something to me. Just now I found this on mugglenet: "We will see more of Draco's mother, Narcissa Malfoy, now that Lucius is busy". This is based on a few online chats they have had with JK and have been announced as fact.
I believe that Narcissa will take over Grimmauld place and prove to be trouble for The Order. I think there may be more... but I just haven't gotten to that. I'm just all excited, I usually don't figure anything out like that :P Of course, this is just a theory, but still... XD