The Deathly Hallows (Mark Spoilers!)

[Ouch!]

Rowling has left Lily and Petunia's background vague for the entire series. We really don't know anything about Lily Potter other than superficial things. Petunia's background (at least in relation to the wizarding society) is equally unexplained. It's almost impossible to deduce what might be important about either of them in relation to Harry's quest. It could be that there are small hints throughout the series that we won't recognize the significance of until we learn what these secrets are. Then again, I recently read an old editorial on mugglenet written shortly after the fourth book which pretty much had the whole horcrux thing figured out based on the diary and one line Voldemort said when he was revived. The person even already had the Harry is a horcrux idea out there.

Harry seems to be a magnet for life debts. I believe that only Wormtail's life debt (as it is the only one specifically mentioned) will be significant, and I can't believe that it won't be paid since Dumbledore mentioned it explicitly. Three Weasleys owe Harry a life debt as well: Ginny (book 2), Arthur (book 5), and Ron (book 6). I wouldn't mind Arthur paying his debt by somehow saving Harry, but Ginny and Ron better not be called on for it.

Edit: In a recent interview, Helen Bonham Carter (Bellatrix Lestrange) announced that Rowling had sent her a letter explaining that her character would be very important in the last book. Ever since her first appearance in Order of the Phoenix, Bellatrix has become a more and more important figure in Voldemort's inner circle. Harry and Neville both have a vendetta against her and she's shown to be very distrustful of Snape. I never thought that she'd be worth sending a letter to Carter when she'd be able to find out for herself in less than two weeks.

By the way, 11 days. <3